Though this is crazy, what would happen if you hung out on Ascension Peak until your characters were level 50?

I would assume that your Fighters/Rogues/Bards/Gadgeteers would have everything maxed except Intelligence (obvious dump stat, since PowerCast won't help them).

Your hybrids would probably also have everything maxed except Intelligence (magic falls off on the peak, and Intelligence, by itself, is a worthless stat).

Your casters would have a choice between Piety, Vitality, and Dexterity. I would go with maxing Piety and Vitality (Iron Will and Iron Skin), as well as having the best hit points, stamina, mana, and carry capacity possible. Note that Dexterity, as the dump stat, gives Reflextion, which your casters shouldn't need, if you keep them out of melee range.

My understanding is that you can keep leveling up, though there's the possibility you might be forced to multiclass.

For slow leveling classes, XP requirements will overflow when you get close to level 50, resulting in that last level taking specifically less XP than would be expected.

As for stats, I believe you can't put more than 3 points into a stat, even if it's the only one not maxed out; this could cause you to miss stat points. Then again, this isn't an issue in practice because you're not going to level to 50 in practice.