People can leave any high-demand Religion or cult if they wish to.
It's what happens afterwards that is important.
Are they excluded/shunned? If not that, are they subjected to emotional manipulation to return to the Religion/cult?
If not emotional manipulation are they criticised? Mocked? Made to understand that they're just not as 'good' as the people still in it?
That's what happens with all high-demand Religions/cults. The beliefs are so important to the people still in it they literally cannot accept apostates in the same way that they would people adhering to doctrine.
It's impossible to true believers.
Apostasy in the Qu'ran is punishable by death.