My question is - can you have the combination of (i) some fundamentalist having access to the nuclear bomb and (ii) not being in power at the same time.

Because using the nuclear bomb, even within its own country, is a guaranteed trigger for retaliation, whether nuclear or more targetted, against that leader/ship controlling the nukes.

If they are rational enough to have the organisation to actually control a nuke, they will be rational enough to try to keep in power. The "fundamentalist"leaders don't go kill themselves, they send others to do it for their political goals. fundamentalism is really a way to control society and to keep power. The fundamentalist and actual believers don't get close to power, because then they are not pious anymore.

In the long run, we're all dead. John Maynard Keynes