Let's be a bit grown up and realistic about this.
BMI are a business quite separate from Teesside Airport, and they are entitled to make whatever business decisions they consider to be most appropriate for themselves. Only time will tell whether pulling Baby out of MME was a good or bad decision.
MME still has the Heathrow link, and Baby's ending of the LGW service may even support that.
If Baby's brief presence at MME has demonstrated that some or all of the routes they offered were popular and viable, then someone else is eventually likely to try and operate them.
Personally, while it was better to have Baby than nobody else, they always struck me as half hearted when it came to using MME, and some of their route strategy was bizarre. If losing them in the short term means getting a more committed operator in the long term, then it may not be a bad thing (just don't expect it to happen overnight).