[Jack Simth]

Shush! Stop giving away the plot before I'm done spinning it yet!

Actually, though, the main reason for Jason's build is a bail-out character; regardless of how bad it gets, he's only perma-gone by DM fiat (Core, it'd take an evil cleric of two levels below twice his ECL to get rid of him for good... and that's likely going to be able to take out the entire party by itself anyway, as it would be level 26 at this point; could also be done with certain save-or-effectively-die Sor/Wiz spells at just a little over the level the party is currently at). At present, he's past his peak level range - about the only ability he has that couldn't be duplicated by a fairly straightforward Sorceror 14 build with an eye towards those abilities would be the Rejuvination, and such a sorceror would have many spells at his disposal (with a higher caster level, and higher level spells) than Jason has available, as well as better saves all around.

Of course, if I accidentally TPK the party, Jason will come back on his own, and perhaps be able to rectify the situation to a degree.