Rea already part of rotation, Brown has been a great asset to the bullpen, and Assad has been beneficial as a SP depth / bullpen arm.
So, you keep what been working with those 3 and go shopping for a guy who can hold it down for however long needed as the 5th starter.
Can't just hope guys will be returning in 2-3 weeks and just try to stay afloat with who they have until then, they take Brown and Assad out of the role theyre doing now, that means they need to weaken the pen and SP depth they have left and will need to add guys like Hollowell, Thornton, etc type to fill out the pen until the injured returns.