Dr_Rictus said:
Any character who sets himself up for that much sorrow when the first dispel magic hits deserves what he gets.
Except of course that the first dispel magic probably fails. d20+10 against a Dc of 26 for a 15th level GMW-xc is not gonna be much of a threat.
Greater dispels are rarer (while i have seen demons and their ilk with SLA-dispel i have seen few with Greater dispel) and then probably only have about a 60-65% chance.
The net result being a slight delay while the spell is recast.
this does not seem like that huge a risk to me.