Msmac

The question of an elective neck dissection usually elicits two disparate responses on OCF. One school of thought says: Better safe than sorry and has the lymph nodes taken out "just in case". They usually post the results that their lymph nodes had no cancer as though that was a good thing instead of proof that they just had unnecessary surgery. Now you can already tell from the tone and tenor of the previous sentences that I am biased and a believer in the school of thought that if there if a biopsy of a lymph node is negative, it's an acceptable risk not to have a neck dissection in order not to severely impact your sympathetic nervous system.
This argument surfaced in a different form decades ago in breast cancer, when many advocated total breast removal or in some cases premptive breast removal, as an "aggressive" treatment. Time and subsequent studies have shifted most medical and public opinion away from that approach. Similarly, most neck dissections are now "modified radical" instead of the old radical method, so less muscle damage and fewer lymph nodes are removed. Still it is not a walk in the park and very serious surgery with life long effects.
In your case, your ENT "is on the fence" and the oral cancer specialist's second opinion "wasn't sure it was necessary". Your signature line indicates that your intial staging was n0 which means there was no indication of the tumor having spread to any lymph node. So IMO, not having a neck dissection if the biopsy is negative is a very reasonable decision especially since your doctors believe that not getting an elective ND is a viable option
As far as factors go , one is what the planned surgery involves. If they can take out your tongue tumor without having to slit open your neck like they need to do for a neck dissection, then your recovery will be quicker if your forego the ND.
finally, if your lymph node biopsy is positive. be sure to ask about getting a modified radical neck dissection
I declined to have an elective neck dissection my first time and when I finally did have one during the salvage surgery, it showed the radiation and chemo had wiped out the cancer in my two nodes, and the rest taken out were healthy. so in the end my neck dissection turned out to be unnecessary.
Charm