He'd still be eligible regardless. As long as he was in GR when the trade deadline expired, he can go back to GR for the playoffs whenever.
As for the timing of the demotions... The Griffins start a week long 4 game western road trip on Thursday that extends well past the end of the Red Wings season. I'm guessing they're leaving tomorrow and the Red Wings wanted those guys to travel with the team for the full trip.
McCollum would've had to go down as soon as Coreau was healthy anway.
It'll be interesting to see if/when Bertuzzi and Coreau go down. FWIW, Coreau will actually have to go on waivers to go back down. That said, Luke Witkowski probably has a better chance at winning the Lady Bing than Coreau does being claimed on waivers in April...
Griffins are leaving this afternoon to Tucson for 2 games this weekend, then head to Austin to play next Wed vs the Texas Stars and then drive to San Antonio to play the Rampage on Thur before flying back home to play their last game of the regular season at home on Sat vs Cleveland.
Hoping this Wings stint will wake Svech up as it is not the GR coaching that is the problem, it is Svech getting too hard on himself by trying to make something happen and it is not happening. With Lorito out for at least the first round, the Griffins need secondary scoring and Svech will be counted out to help out in that department.
Coreau should not have any problems clearing waivers with his performance with the Wings. According to Nelson, Bertuzzi will end up in GR for the playoffs, unless he gets an injury in the final games in Detroit. The Wings are wanting the Griffins to get in the playoffs and they are willing to do what they can to help the Griffins out. That is what Nelson said in a post game interview in the Griffins last home game.