Can I replace a single breaker with a double in the space above where broken tab is
Here is a few things to consider. First a QO double pole breaker usually has only one connection point to the tabs. So make sure it's on the correct side. 

Second, and I know this might be nitpicking but NEC Article 110.12(B) Integrity of Electrical Equipment and Connections states there shall be no damaged parts that may adversely affect the safe operation or mechanical strength of the equipment such as parts that are broken; bent; cut; or deteriorated by corrosion, chemical action, or overheating. 

So the question is: Does that fit this situation? Which I cannot answer because I am not there. What I will tell you that is I if I were still running a service company, I would have a liability to my customer and my state license. I would replace it.

I am not sure of the age of the panel but you might be able to find a comparable box where the guts match and just replace the guts rather than the whole panel.

Whatever you decide use good judgement and be safe.