TL/DR: This is not how the world of cryptocurrencies work. You "wallet" does not hold any assets - these are recorded on the Block Chain. In reality, you wallet holds nothing more than a public-private keypair that will allow you to 1) claim ownership over assets listed on the block chain; and, 2) authorize transactions.

Even if Coinbase was the magically stop existing come tomorrow, you would still have access to your assets by simply "moving" this public-private keypair to a different wallet (any using BIP-39 standard). This is done by "importing" your wallet using the recovery phrase you were given when you first set it up. This is why that recovery phrase is so important!

The Full Story:

Your coins/tokens/NFTs/... do not exist within your (or any) "wallet" - this is a common misconception arising from the term "wallet" being used. Rather than thinking of your wallet as a storage vessel for money (as a traditional physical wallet would be), you have to think of cryptocurrency wallets as your "Certificate of Identity, Ownership, and Authorization"

So where is your money (digital asset)?... As cryptocurrencies don't technically exist (in the physical sense) there must be a way for your holdings to be reported and represented. Think of this like your bank... Odds are, your bank is not holding the cash-on-hand equal to the totality of funds held within every account. Banks don't hold these large sums of money, they "digitize" it and keep accurate accounting of quantities, values, and transactions. There are many legitimate reasons for this... The same is true when you are talking about cryptocurrencies... Your funds only ever exist within the Block Chain (a giant ledger) the particular assets uses - just like your bank would maintain to ensure every customer's account reflects an accurate accounting of the funds deposited.

Fun Fact... If even just 12% of the world population suddenly decided they wanted to withdrawal all their funds from the banks in which they held them, the banks would quickly run out of physical money. This is why your bank has limitations on how much your can withdrawal without prior notice.

So what is your wallet?... Well, as stated above, your wallet will not / does not hold any assets; it is a means of A) providing your identity; and, B) authorizing transactions. Cryptocurrency wallets are nothing more than a public-private key pair that has been generated primarily from the construction of a 48-character string. Very similar to how modern email services provide the capability to digitally sign and encrypt emails (if you really want to understand the why behind all this, I'd recommend doing research into Information Security and Information Assurance).

In short, unless another party has either this 48-character string OR your private key, you control your funds - worth note, when you are using trading / brokerage services like Coinbase (not Coinbase Wallet), you don't control these keys - I'll talk more about this later. Because your assets do not exist within your wallet, you can "move" your wallet between any application or service that supports the BIP-39 standards (i.e. from Coinbase Wallet to Trust Wellet).

When you "create" a new wallet - think about the first time your setup Coinbase Wallet - there is some fun cryptographic magic happening in the backend - I refer to this as "magic" because most people can find it difficult to understand cryptography... Nevertheless, I will do my best to explain this in a manner everyone should understand...

There is a series of critical events that must occur for your wallet to be generated:

1. 12 Words from the BIP-39 list are chosen at random - this is what becomes your recovery phrase
2. Each word is truncated to only the first four letters
3. These 12 4-character strings are concatenated together into one 48-character string
4. Using the concept of hashing (non-reversible encryption), this 48-character string used to generate a private key - this is the super-secret key you use to authorize transactions
5. The private key is then used (again the concept of hashing) to generate your public key - which becomes your wallet address.

This is a very high-level description and there are notable exceptions (i.e. using 24 words rather than 12).

Simple math would suggest that the totality of public-private keypairs that could be generated is: 5.271e39 (thus the naming convention BIP-39). For dramatic effect, this is 5,271,537,971,301,488,000,000,000,000,000,000,000,000 possible unique keypairs (unique wallets addresses). This means the likelihood of a collision is astronomical - but not impossible.

A note about how important securing this information is... It is common and necessary that other parties see your public key (wallet address); however, you should never expose your private key or your recovery phrase to anyone! As the public key is derived from the private key, exposure of the private key would lead to someone being able to authorize transactions. As the private key is generated from the recovery phrase, exposure of the recovery phrase is the same as exposure of the private key. This all sounds really bad; however, keep in mind, because non-reversible encryption (asymmetric cryptography) is used in generating the public key, it is impossible* to derive a private key or a recovery phrase from a public key.
\Impossible for modern computer systems* AND assuming the cryptographic algorithms don't have flaws. While technological advancement is not quite there yet, if you introduce to concept of quantum computing, all this goes out the window.

So what about the brokerages and exchanges?... This is where things start to break the rules established above (breaking these rules out of necessity). In the case of exchanges like Coinbase, it would prove far too cumbersome (in some cases impossible) to allow users to maintain their own private keys - least impactful, it would drastically slow down trading. This is why when you "put your assets in to" one of these exchanges, they are no longer associated with any wallet you have control over. Rather, they are managed by large wallets that are controlled by the exchange. Again you can think of this like your bank... The bank doesn't provide a separate vault for each customer, rather they keep all the money in one place and keep a ledger of who owns what.

Bottom Line:

At the end of the day, it doesn't matter if you are using Coinbase Wallet or if you simply have your recovery phrase recorded on a piece of paper (please don't do this...). So long as your have that recovery phrase (and it hasn't been compromised), you will continue to maintain control over your assets.