I dont think that door is closed completely, but it's damn close. There's not much point in trying to stretch him back into a starter if he only hits like 60 innings this season and would then only be good for 90-110 innings next year as a starter.
His only real shot at getting back as a starter is doing a lot of multi-inning relief this season, with no health problems, and gets 100+ innings IMO so that if they wanted to, and his health held up, they could try for 140 IP next season. Lots of IFs.
And he went 2 innings today, so... that's obviously what they are thinking and hoping also.