Guh... I'm never good at guessing these things... ^-^;
I say that it'll evolve. I don't know why, but I just think that it would be silly to showcase the evolved form of one of Ash's pokemon again. Not that it can't happen-- *coughRaichucough* --but I just think it unlikely.
Grovyle evolving might change it, and it might not. Look at Chikorita, it hadn't changed much at all when it evolved, she was still leaping onto Ash and fawning over him. It took a fight with Ash to change her. Of course, the change from Treecko to Grovyle made its personality a little different, but not real different. I mean, it was a little less aloof, but this might have just been the result of getting to know everyone better. *shrug*
I would like to see one of Ash's pokemon evolve and overtake him in knowledge. A pokemon with a sort of wiser look/act about it would be a nice addition to the carefree, happy pokemon that Ash has now, and I could actually see it working with Sceptile. Treecko's always had this air of superiority about it, so to become a very wise pokemon would be an easy transition.
Eh... hopefully that made some sense... It's like 6:00 in the morning here... >.>
Oh, and you're right DarkWeezing, it is truly a crapshoot. *nods*