The Mickey fingers have been out of show for some time now...and probably some time to come. Apparently there was an incident. There's also some other pyro changes as of late due to incidents.
For Fantasmic!...a projector failure in front of a completely full section of the audience is a show stop and possible show cancellation. Most of the show is film and it also masks scene changes and show/character integrity pieces. Fantasmic! in Florida is still 70mm film...and you cannot rewind film and start over...the whole film has to play back through to the beginning. So if the issues there that night couldn't be immediately fixed, it would have been likely a show cancellation.
Disneyland doesn't have that issue...they run digital projection...so they avoid the intricacies of film.
I know they used to have a projector maintenance person on the island to fix things. Rumor has it s/he got stationed somewhere else due to budget cuts.
So preventable? Yes. All comes down to the almighty dollar. Not sure when enough is enough, and they finally decide to inject some money into this almost 15 year show that has NEVER had a proper refurbishment. It appears from reading other posts and listening around that Fantasmic!...while still operating every night...is in a state of massive disrepair. And it even looks like it's falling apart. Many of the technologies are far behind its big sister in California. But isn't that always the case?
Then again, why should they inject money into something that still fills up the amphitheater night after night? I see the "sorry for the technical difficulties, it's out of our control" excuse thrown around far too much these days...
"Its out of our control" usually really means "We didn't maintain it well enough, and we didn't replace something when its duty/life cycle was complete"