Dudas

If I create a strategy, I can save it as an EA with mq4 extension, so far, I agree, but if for whatever reason I lose the mq4 of the strategy created to make any modification, how can I recover it through ex4, which is the only thing that would stay ??

There is no way to get the source code from the EX4 file, you need to keep the MQ4 source code stored