They will just pretend to be some other religion.
"According to sharia, in certain situations, deception – also known as 'taqiyya', based on Quranic terminology, – is not only permitted but sometimes obligatory. For instance, contrary to early Christian history, Muslims who must choose between either recanting Islam or being put to death are not only permitted to lie by pretending to have apostatized, but many jurists have decreed that, according to Quran 4:29, Muslims are obligated to lie in such instances." https://www.meforum.org/20...

Muslims are allowed to lie to unbelievers in order to defeat them. There are several forms:

Taqiyya - Saying something that isn't true as it relates to the Muslim identity.

Kitman - Lying by omission. An example would be when Muslim apologists quote only a fragment of verse 5:32 (that if anyone kills "it shall be as if he had killed all mankind") while neglecting to mention that the rest of the verse (and the next) mandate murder in undefined cases of "corruption" and "mischief."

Tawriya - Intentionally creating a false impression.

Muruna - 'Blending in' by setting aside some practices of Islam or Sharia in order to advance others.