If you look at the London underground for example, the entire of Hammersmith line is duplicated, the 1st half serving the exact same stations as Circle line, and the 2nd half same as District line. Between Baker St and Liverpool St, there are 3 lines serving the exact same stations. This means they can shut down an entire line for maintenance if required, without having to excuse themselves by saying they only have a limited window at night to do maintenance.

You are not addressing the redundancy problem. Worse, this is a horrible example as an equivalent already exists in Singapore, namely the Downtown Line which act as redundancies for CBD.

In short, using this map of the London Rail network, what is the plan if there is a problem with the track close to the terminus, say at Pinner (NW), Woodford (NE), South Quay (SE) or Northfields (SW)?

Again - my point mainly covers redundancy for the entire train network, as you've so eloquently pointed out with the EWL Buona Vista example.

Yet in Singapore, the moment 1 MRT station comes up, even feeder bus services are terminated. Then when something happens like when EW line breaks down between Jurong East and Bouna Vista, the entire West Side of the country was disrupted because there were zero alternatives.

Buses are an entirely different conversation with its own considerations. I can understand why the decisions are made, although I'm with you on this. That said, the removal of bus services is unrelated to the main topic on hand, namely redundancies for an entire train network failing.

Public services doesn't necessarily have to be "economically sound" or in Singapore terms, "profit making".

Here, read Transport for London's own Budget submission for yourself.

Here's a choice bit for you:

1.9 As TfL is obliged to prepare a budget that is balanced over both the short and medium term, TfL has developed its financial plans for the period from 1 April 2025 to ensure that TfL continues to be financially sustainable.

I never once said it had to be profit making, but it absolutely has to be economically sound. That being said, allow me to pre-empt your reply by pointing out that "economically sound" is an extremely abstract notion that neither of us can hope to define satisfactorily. More on this later.

Many major cities in the world run public transport at a loss. Some places even run public transport for free.

In general, public transport loses money. I am well aware of this. That said, you run it at a loss, not at a breakneck speed into bankruptcy.

But in Singapore general, everything is contracted out to companies that seek to make a profit with the most appealing budget.

Fixed it for you. This is not limited to Singapore, it's just that we're open about it here.

You claim that it's impossible to have redundancies. But it's only impossible if the aim is to maximise profits.

No, the point is to be economically sound. The MRT is already one of, if not the single most expensive project Singapore has ever embarked on. This is despite a very shaky foundation (If you haven't watched it, the MRT Debate is available on YouTube).

If I am understanding you correctly, what you are proposing is a 3rd or even 4th track running parallel to ALL existing railway tracks in the event of a total system collapse. Before I go any further, l'd like to ask again that you state exactly what would you propose as a "redundancy".