It really isn't going to be an issue for a variety of reasons.
1.) The Herald is born alone, and is an easy kill detached from a unit.
2.) He has to deep strike in when summoned and it has to be within 6" range of the psyker, so a mishap is pretty likely compared to the other powers.
3.) People don't own that many Herald models (and if you don't count boxes of regular daemons people CALL Heralds, this matters more, of course).
One thing to remember here is that even if one or two people did this, it's not really a big deal, regardless -- it's not worth reacting to just for one or two corner cases, I think.