Even without serious injuries, there might be some with minor injuries, in which case they very well should go after Disney. Even with a minor hit, there can still be minor injuries that would mean PT is needed at home, probably follow up with primary care doctors, lost wages for doctors appointments and PT, plus a sum of cash for pain and suffering...if you have no damages, then don't sue, but if you have and can prove damages, you should sue. If this were a regular traffic accident at home, you would sue.
A lot of lawsuits are frivolous, but the one driver was ticketed, and for those 15 people who went to the hospital, they should sue. Not for millions of dollars, but they should settle with Disney for damages.