Probably wouldn't have amounted to much, though. If Signetics had patented it, purchasing it from him, he would have gotten what, maybe a few hundred dollars? That's about what most engineers receive for their patents from the employing company.
Now, if he had left Signetics and founded another company to create the 555, then he might have been rolling in dough.
But instead he created a company that pioneered the concept of semi-custom integrated circuits, and rolled in the dough. :) I think the mentality that he was somehow cheated out of something would have been seriously lost on him. He did what he did because he loved it and the money was secondary.
Now, if he had left Signetics and founded another company to create the 555, then he might have been rolling in dough.