A couple of more shots like those at the end of the forth and Brewster's corner would have waved it off then, or the referee wouldn't have let him take anymore.
It wouldn't matter if Lamon refused to quit tonight - it would have just kept going on the same way. Brewster needs Wlad to punch himself out with power shots like Wlad did in the first fight but Wlad has become to smart and ring savy for that. Tonight's Wlad beats any concievable version of Brewster under any set of circumstances, simple as that.
Brewster was fit as can be and looked strong and dangerous coming into the ring, difference this time is that Wlad fought his fight, had it gone another round or so Brewster would have been out cold. Brewster had a better shot vs any of the other champs or should have fought Briggs before Sultan did