Is it permissible to decrypt a Forex indicator for personal use, after the programmer distributed it for free then it stopped working due to its expiration date, and it was impossible to contact him for permission or to purchase it?

It is not permissible to copy protected software except with the permission of its owners, because intellectual property rights are recognized. If the programmer of the indicator made it available for a specific period or to a specific group, then it is not permissible to exceed that. However, if he made it available to users absolutely and did not reserve the right to copy for himself, then there is no harm in decrypting it for personal use.