Remember that Tervigon's can only replenish Fleshborer models, so you probably don't want too many devourers.
I'd consider perhaps running one block of 30 Termagants (all Fleshborers) and a basic Tervigon, then spend the last 200 points on Warriors to lend a bit more shooting and some melee capability (can get 8 with Boneswords/Deathspitters).
List #1 Patrol:
List #2 Battalion (MSU
I do think regardless one does want to keep the Termagant unit fairly large. It isn't hard to loose 15-20 in one go but as long as you have at least one left you can replenish them.