How could I fix up some old plaster
In older structural brick buildings, it was relatively common to plaster directly to the exterior brick walls.   Most of this plaster has successfully held for 100+ years, so if you were to simply remove the loose plaster and re-plaster I would imagine that it would hold for quite a long time as well.

However it plastering is a bit of a lost art and can be very time consuming and expensive.  You could also install some furring strips directly over the existing walls and ceilings and drywall.

I guess the decision would depend on if your goal is to retain the current plaster, or simply to have functional walls and ceilings.   It almost always works out to be less expensive to install furring strips and drywall.   Also depending on the situation this gives you an opportunity to add some insulation.