New to Zwift, love the pace partners!
I was riding behind Maria for 1/2hr or so, fell off the back maybe 30m and pushed hard to get back to the group. Never saw her again and then there were dozens of riders stopped on the side of the road. Did the ride end? I know they change routes on Mondays, but this was Tuesday. Thanks!
Maybe that one went on a different route from the one you were on, assuming you just joined them as they came past rather than joining them from the main screen.
The RoboPacers don’t stop as such. They used to have occasional short maintenance resets IIRC (once per day?) but I’m not sure that even happens any more.
It could also be that despite pushing hard, you just didn’t have the speed to close the gap. The draft effect means that the RoboPacer blob generally moves faster than the given power output would suggest.
There are always plenty of riders stopped at the side of the road in certain spots, as these are the drop-in locations for people starting a ride on various routes. e.g. along the Watopia coast, another one in the desert, one at the start of Road to Sky, etc.
Just end your ride and rejoin. Don’t bother trying to chase back on unless you want that type of work out.
Oh, and the pace bots do quit. Happens late Sunday night usually. Probably to switch routes.
Yesterday Yumi had a pee brake for 2 minutes on Volcano top 
Genie today gave up on a sprint segment. The group was going at normal pace and suddenly Genie dropped back very rapidly as if the bot had no draft ability. And the bot never ever managed to catch up again. 
I’ll put that one to some strange glitch because Genie was keeping with us for the previous 25km.
Hey, this happened again this morning (~7am PST) on Big Foothills, Yumi disappeared on the Volcano descent and then was 2 minutes behind. Maybe she needs to change her ebike battery up there after the long climb?
Genie suddenly passed the Turing Test and realized she wasn’t being paid enough for this ****.