Your theme developer is not in the geocoding and locator business primarily are they? Either way, pointing fingers is futile. We did NOT change the Google MAP API key or how the jquery worked. Since you are keeping that theme there is not much of an alternative regarding SLP or any other locator /map plugin that uses google MAP API. We always suggest that any site, (especially one with clients), have back-ups and/or a virtual site to test on before updating themes or plugins. That way you can see what changes will happen and roll back if needed.
Now we are off subject of this post and I will need to close it.
P.S. If you have multiple clients using SLP, you are required to have the Premier Subscription.