He's cheap, no need to move him - plus Gillies is waiver exempt and hasn't really outplayed Rittich yet. Why would Calgary trade him now? Makes zero sense.
Scenarios:
- he'll be bad. You'd get nothing for him now and you'd get nothing for him later. You can just as well wait to see if he's actually any good.
- he'll be better than Gillies and a capable backup. You keep him.
- both Rittich and Gillies turn out good but Gillies is better/younger/whatever. You can either keep Rittich as insurance for the playoffs, or you can sell him at the deadline for a better pick - maybe a fourth rounder, depending on need and his level of play, better than what you'd get now.
- bonus scenario/variation of the above: a team loses a goalie mid-season and desperately needs a replacement. Again, you trade him for a pick or an okay prospect and get something back.
You trade him now, you get nothing. You wait, you may get nothing, but you could also get a mid-round pick or an NHL backup. Seems like a no-brainer for me.
You could try trading him for a more proven but expensive backup to a team with a cap issue. Can't think of any team from the top of my head but that's honestly the only scenario where I could see trading him in the summer.