At the end of last season this happened and all that was left on the enemy team was Mercy. My friend was Reaper and I was Mercy and we were being friendly however the Pharah on our team was not so we just emoted and said hey through spawn (she wouldn't let her out let alone on the payload). I felt bad she had been abandoned At one point someone came back, took Rein, died as soon as they left spawn then left again.
I hope you find a better team that don't jump ship at the first sign of sinking.