The legendary band played their last gig Saturday night at Madison Square Garden -- this as part of their 'End of the Road' farewell tour ... which marked their final live performance ever. Or so everybody thought, anyway -- 'cause they say they're keeping the party going.

Rather than continue to sing and dance themselves, Gene Simmons and co. are gonna let their AI counterparts do it for them ... in the form of computerized avatars that can keep on playing shows quite literally forever. It's called KISS Online ... and it marks their new era.

The whole thing might sound goofy, but it's actually a trend that legacy bands are starting to embrace more and more -- including ABBA, which has recently trotted out their own digital avatars in full concert ... and playing to packed crowds, no less.

The guys simply put on motion capture suits and recorded a full-blown concert of theirs ... which can then be repurposed and re-aired for years to come ... with cool effects and stunts they wouldn't normally be able to do on their own (especially at their age).

The KISS avatars actually came out onstage Saturday during an encore ... and performed "God Gave Rock and Roll to You" ... but they only did so onscreen, as opposed to appearing as full-blown life-size holograms. Time will tell if those holograms will debut at some point.

Anyway, it's certainly the end of an era and the beginning of a new one. As you can imagine -- there are mixed reactions to the news ... some hate it, others are fine with digital KISS.

It also serves as yet another reminder that we are very much living in the future right now ... with the way tech/AI is going -- more and more stuff like this is going to be introduced.