Those are both reasonable approaches. The reason I would approach it differently is that both bacteria and NH4 adsorbing resin is very specific in what it'll do. In an established tank that had a death and an ammonia spike these would be on my list too. But in the case of a disturbed older sand bed liberating stuff into the system, I think there's more than just ammonia toxicity to consider and we don't actually test for a lot of stuff that could be causing trouble. Water changes will dilute the nasties over time along with carbon (not too much, watch the ph) heavy, wet skimming (yum!) and time.