Joshua E. Lane, MD, MBA

This is difficult to answer without more history and without a clinical exam.  Even if a nerve is transected/cut, it should not cause lifelong nerve pain.  I would recommend either examination from the surgeon who did the Mohs surgery or from someone else.  There are reasons that can cause nerve pain that warrant investigation.

These are two different CO2 lasers from competing companies - both lasers are excellent and likely the two best for fractional CO2 resurfacing.  I have used both but I currently have the Re:pair.  Many factors go into the depth of penetration, mainly however the settings that the physician dials in.  Not all patients need or can tolerate the deepest depth of penetration.  You are correct that the facial Re:pair handpiece is 0.135 µm...the "body" handpiece is 600 µm and is used with less penetration.

This is a niche treatment in that it requires a specific laser to treat, knowledge/experience to do so, and willingness of a treating physician to do so.  The procedure is not difficult for those who perform it - it is just a matter of finding the right person who does it.  Ablative CO2 laser is likely the most effective means to treat this - while fractional CO2 laser is common, less surgeons use truly ablative CO2 laser than in the past.  

Without a photo this is very difficult to answer; however, you are likely correct in that a dissolving suture is the most likely culprit.  These are typically cream colored or clear...you can likely just pull it out but the safest answer would be to go have your surgeon evaluate it.

A cellular dermatofibroma in itself is not necessarily a problem; however, the pathology report may indicate some degree of cellular atypia, which is likely the reason your dermatologist is recommending excision/re-excision.  If there is no atypia, these are often persistent/recurrent which is another possible reason.  Mohs surgery is not typically appropriate or necessary for this.  I am fellowship-trained in Mohs surgery and thus can speak from experience about this.  In rare cases where the lesion is very atypical, that could be a rare reason to perform Mohs - but in general a standard excision is the treatment of choice and appropriate one.  What you have scheduled sounds perfectly normal and appropriate.  As to your question regarding the cells still present...they are just that...they are just there which is why they want to remove the lesion in entirety.