Trach stoma not closing

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My brother had a neck surgery last year, requiring a tracheotomy for over ten months.  The trach tube was removed, and he was told due that, due to his age and diabetes and how long he had the trach, it might take a month or more for the stoma to heal over. Four months later, it shows no signs of closing. It is like the earring hole in your ears, basically permanent, as far as I can see. What can be done? Can it be debrided or facilitated surgically somehow?
The next problem is that, if he was weaned before they removed the trach, the weaning has reversed. He breathes only through the trach stoma, and for the past 4 months, that is room air filtered only by the gauze dressing.
Would you recommend starting over? Replacing the trach so it can be capped for training mouth/nose breathing or using a Passy Muir or another standard weaning protocol?  I am afraid the stoma has no chance of healing over if it is his primary airway.
Thanks for your advice.