His "injury proneness" has been wildly exaggerated. There is risk with all goalies, and I'm not sure on what basis you're suggesting that Dubas wasn't aware of Mrazek's history? Just because a goalie has been injured in the past, it doesn't mean every GM that signs him after that is stupid, which seems to be your suggestion. His injuries are probably why we were able to get him for only 3.8m on a shorter term. Mrazek has some of the best medical resources available to him here, and should be able to play for a good portion of the season, behind a good team and defense. All it takes is a simple look at the goalie market to see that Dubas shouldn't have any trouble moving Mrazek in the offseason, if it comes to that, unless he completely bombs upon his return, which is unlikely.
Heck, Andersen is 32, completely bombed last year+, and has dealt with multiple injuries over the past couple years, and he still had teams willing to pay him more than Mrazek.
No, he most certainly did not.