When someone quits a band, it is never unexpected.. There are hints that there will be a change..

I left our band after 12 years, but still sub once in a while..

There were no surprises that I was about to leave.. Boredom is usually the culprit..

My case traveling 200 miles to and from a gig , 3, 4, and 5 times a week..

When I joined the trio, they were use to using floppies with a Yamaha sequencer for tracks.

I improved performance immediately.. I also recorded tracks with real vocal backings.. the lead guy and gal are great singers.... The over all sound was the best.. and we were soon the most popular shore band in South Jersey..

When I left them they were in good shape... I taught them how to operate the gear.. left capable gear with them.. and made sure they had a back up plan to add someone..
I also developed the band website and maintained it..

You can quit without burning your bridges... honesty and integrity are the keys..