Just thinking out loud, but maybe wouldn't it have been better to just demote Grebs, instead of conditioning stint. Here's my thinking.
It's his first year back in the NHL, and his pre-season wasn't great, and he got injured. If they just assign him outright, he probably doesn't get picked up with those circumstances and I'm not hearing many teams desperate for 6/7 d-man at the moment.
Grebs loses no money, but Edmonton gains about $5K of cap space per day that he is down. If his stint goes well, you just bring him up like you would have on a conditioning stint. If it doesn't keep saving the capspace until he's ready. This also would give the benefit that should they bring him back up, they can send him back down without waivers within a month if they need to.
The same applies to Potter when he returns. If you could get 3 NHLish d-man normally vulnerable to waivers, free from the waiver wire for a month by squeezing them through when they are least appealing ,in what is essentially a 5 month waiver period, the Oilers would be in pretty good shape to handle future injuries to the blue.