A loose rule of thumb for Boeings without fuel dump(75,73 etc)is that if you can take off from any given runway you can land back on it.If you are a real stickler for graphs you can consult Boeings amazing fractured incomprehensible complicated disjointed landing performance data.By the time you get an answer you will run out of fuel .Overweight landing inspection-not a huge issue compared to a full accident clean up.
Your companies attitude is shameful and they really deserve to be named and shamed.Ask the guy to imagine sitting in the back with his kids as you explained over the PA that you had a very worrying engine problem but had decided to continue on the basis that it might be alright.Record all your conversations with this guy.