Surely this (unlike many other environmental and social issues) is effectively solved by price?

If helium balloons cost $100 each vastly fewer of them would be sold. If they cost $100 but you could get $90 back by bringing them back to the store for the helium to be recycled, much less helium would be consumed.

If there is a limited supply of helium for essential medical use, the price should rise until either demand is affected or less of it gets discarded by hydrocarbon extractors. If this doesn't happen we are probably ok.