Not sure I understand your point.
Yes, that OLD, can't be kept up to date, will be gone, that is IF you delete it, BUT the 'new one' that CAN be updated using the Sync feature, will keep the new tree up to date when others find it.
I would prefer to find an up to date tree, not one that can't be updated. But, that is your call.
I put my tree up, and IF this happens, I just Delete the Online Tree.
OH, IF you have contributors or editors on your old tree, you will have to invite them to the New Tree. BUT, you don't have to recreate who you invite, as they will still be in your profile for other AMT's that you might have.