I do not think any manager could do anything with these players. Some of the problems with the squad fall at Lambert's feet, but I actually think the good majority of Lambert's signings (Benteke, Vlaar, Lowton, Westwood) have been positives.
That being said, something had to change just to shake up the team. If Learner does not want to spend any money, he has to get rid of Lambert. If he wants to spend money, they need to do it now.