There are many reasons why a firm might withdraw. The fact that disclosure could be detrimental to their former client suggests that the client lied to them, to the court or that there is information that the firm learned that created a conflict with an existing client. It is impossible to tell without knowing more facts.
Most of the time, a summary judgment motion should be filed when you have completed sufficient discovery to determine that they do not have a defense to certain of your claims. In this setting, if you file a MSJ now, the court will surely give them time to retain counsel and respond. If the motion was pending and this happened, the Court might give them a shorter rope. Filing a motion for summary judgment prematurely will telegraph your facts and allow them to respond to future discovery in a manner designed to create issues of fact that are tailored to defeat your motion. Further, if discovery is not complete, they will file a 56(F) motion for additional time to complete discovery so that they can respond to your motion.
I strongly recommend that you retain counsel. By asking this question, you demonstrate you are not equipped to handle this type of litigation. Best of luck.
This information is not legal advice. It is for general knowledge purposes only and cannot be relied on as legal advice.