I think the main issue with tail 1st decay is the weird effect on range. Without the head decaying you get this weird marching ants effect as you decide not to add to a worm because you don't want it to be infinitely long. Then it also creates a weird worm farming mini-game as you keep worms alive - which although fun, is a waste of fuel.
I would prefer a different type of block to the worm gun for something like this. Either something that unpacks itself, so tail 1st decay has less weirdness, or perhaps make a bullet based on bugs that has a weird effect on rocks (astro-fac could redeem itself).