Grading unsuccessful team work in a seminar
This post might be relevant to you: Should I hide the fact that I did a group assignment completely by myself?

Regarding your question:

You put them together a few months ago, and still you only get a complaint a few days before the deadline. Now, there are two possible cases:


They don't have a finished report by the deadline. In this case, I would take the appropriate steps. They had months to discuss the topic with you, to get into another team, etc., if they only come to you five days before the end, they have to take the consequences.
They have a finished report, but one of them claims to have done most of the work. In this case, you already took good steps, I would continue along this path. If the student doesn't answer, assume he dropped the course and act accordingly.


Regarding your evaluation, you should know that it is common for students who get a bad grade (like it might be the case for the lazy student here) to give a bad evaluation. The people reading these evaluations should also be aware about this and as long as it is only a single one that stands out negatively, it shouldn't affect you too much. Be prepared to explain and justify the steps you have taken, e.g. offering the students to split.