limits to the use of experts

[Britrade]

I would like to ask a question. If the constructor of an Ea leaves the mql5 community, will I be able to continue using the Ea purchased?

[Samuel Akinbowale]

yes
if you buy it or your rent is still valid

[Michael Maggi]

This is only if you purchase. Rentals require payments and if the Signal renter left MQL5 community, the Seller relationship would have ended and the signal would not be available.

If you purchased the EA or indicator through Market and it requires to check you are a registered user then it might also stop working.  Some of these things depend on the way the EA/Indicator author configured the security to protect their copyright.