The thing is that it didn't seem like that at the time. Someone high up went around the company to see if there was a fit for me, claimed there wasn't, and then said I could either give up on the technology or go work somewhere else. An offer came in around then to do so, I took it. Ironically, that person ultimately left Google arguably over the consequences of adopting that technology later on.
I personally know several people who have left & come back up.
If you left on bad terms, then of course any company wouldn't want you back.