Everything is ultimately a dead end. You can thank entropy for that. The sun will die, too, as will any star we go to.

Fusion would probably be the best, because a large fraction of the universe's mass is hydrogen. Antimatter would also be cool, but it's also incredibly dangerous and we're far from being able to create significant amounts of it.

In the long run, we probably can't afford to drop any power sources. But in the long run, we're all dead.

There are large quantities of fissable materials which are not uranium. For example take thorium, which is roughly as common as lead.