If they make gathering chains carry over then make it where after say 4 successful gathers the chain lasts 90 secs or until an unsucceful gather or until you gather a different item.

For example:
Player X gathers iron 4 times gets 90 sec chain bonus player X fails to gather iron on attempt 5 chain broken.
Or
Player X gathers ice shard 4 times gets 90 second chain, player x gathers iron on 5th attempt chain broken

But with this implement you should change the max gathering % to 95% so there is always a chance for failure