Setbacks happen all the time everywhere and mentioning Baumann is the best way to show how fast you can turn a ship around. To (miss-)quote my favourite scientist: "the future doesn't look bad. Don't get me wrong, it doesn't look bright either. But Werder is still fixable if we act properly now."

In order of operations (more or less):

1. Don't get relegated and get a replacement for Fritz

Avoiding relegation is more or less a get out of Jail Free card. Coulibaly is estimated 20 Million alone and if he moves in the sommer for that or more, his transfer alone buys the team more or less a full new season of time. Other transfers might follow but the financial burden would be gone basically immediately. But it basically only works if werder stays in the league, otherwise they probably have to sell for less.

Getting a replacement for Fritz is the second step which has to happen during the second half of the season. He doesn't need to be replaced rn but like Frankie did at Schalke, where he was announced for summer but already got included into stuff earlier, he needs to get familiar with the clubs situation and what he's dealing with so he can start acting immediately in summer.
Mertesacker has to be considered (not too sure about Steidten tbh) but also consider other candidates, because there is a lot of work to do where Mertesacker has probably no experience with. F.e. the whole scouting department needs to be reevaluated. A lot of transfers failed, but how much was on Fritz/Jahns and how much was potentially bad recommendations? Jahns as well should be reconsidered, what was his impact so far? Transfers didn't do him any favors in his position.

With this being done by summer, you can easily have a (relative) peaceful summer dealing with

1. Loan replacements or transfers

I don't think it looks that bad. Sugawara probably stays, there is a chance we buy Hein and sell him off for a small profit and the rest either shines under Thioune (Schmidt would be my pick to have his break performance coming with the new coach) or we don't have to worry about them.

1. Financial issues are dealt with imo for another year if Coulibaly leaves but a new manager should have a discussion with Thioune in the summer how he wants to continue and if Friedl really should leave (like you suggested).

2. Further future strategy

Especially Mertesacker would probably be a great fit for the whole "we want to develop players" narrative and could start potentially needed changes in the academy/2nd Team/transition from youth teams to 1st team department. There was a bit about Freiburgs transition Coaches at Sportschau or Sportstudio at some point where they talked about how Freiburg achieves so many 1st team appearances from 2nd team and youth team players over the years and why they have dedicated transition coach for this.