"Who else would have the guts to tell the tribe that if they look for the HII everyone's putting their name down?"
That's actually a stupid move, if played straight. You'd want the person holding the idol not to expect votes against them, or to be confused as to which one, them or their allies, is being targeted. Going straight after them almost ensures a bounceback. Not that Sandra cares, being a cockroach, capable of surviving the collapse of any number of alliances.
If it's meant as a deterrent, I don't see it working, either. Those afraid of holding the idol aren't usually the ones to look hard for it, anyway.
"I think he and Colby are good until merge now"
I think JT's more than willing to switch back. His move was all about getting rid of his rival for dominance of the majority alliance, as you indicated. Why team up with another natural leader (albeit of a different kind)? He'll swoop in and claim Amanda et al for himself, I predict.
"The idol has no power if your whole tribe comes gunning for you."
Actually, the idol has greater than average power if the whole tribe is gunning for you. Unless you don't know they're gunning for you. Except they told him, so he does know.
There's always vote-splitting, which could hurt your alliance. But I don't know if that falls under the umbrella of "your whole tribe gunning for you" as it's been presented. Also, vote-splits can be torpedoed, as demonstrated by Cirie's ouster. in fact, I find it exceedingly odd that you place Russell at the bottom when all he's doing is exactly what Tom did (i.e. looking for the idol in the open), given that it worked well for Tom.
If Russell were not to find the idol before the next tribal council, I would agree with what seems to be the prevailing opinion that Russell's screwing himself. However, I predict he will find it, they will target him, and he will somehow use it to gain control (along with his alliance) of the tribe.