[PSA] Its very likely safe to play TF2 right now. An RCE existing is extremely unlikely.
First of all, the source code being leaked doesnt mean much when it has been known by hackers for ages, which was the source of the lag/crash bots. If an RCE exploit existed, it would've been used a long time ago, or would've been reported to valve for a couple thousand dollars.
A take from a professional, who has earned a lot of money finding 0-day exploits in programs such as Filezilla
Teamwork.tf's opinion on the situation
However, it is not unwise to just wait out an official response from the TF2 team, much like we did with the official CS:GO twitter account.
Also for those unaware, it has been proven that the images that were shown here a while back where a pop-up saying that cathook was getting into your account were fake.
Also this: Apparently the leaked code isn't strictly TF2 source code, but just code shared by TF2 and csgo -> Posted by a Steam community forum mod