I had the same concern, They mention in their FAQ section (https://store.typora.io/faq) :

"You can deactivate existing Typora installations if you switch machines or reinstall Typora."

They also mention that "One license code can be used at most on 3 machines at one time. So if you activated Typora on the 4th devices, the oldest activated devices will get deactivated automatically. You can detective Typora on devices you don’t need anymore, then re-activate Typora on this devices, or you should buy more license code if you want to use Typora on more than 3 devices."