IMO participation in international events is of no importance - we probably have about 30 "regular" DBMM players here in NZ butsome of them only play occasionally - but that's enough to keep going as far as I'm concerned - even if only a few of them are local to me.
the "secret" to continuing is to just do what you can and not trying to become a DBM replacement overnight - as long as you can get a handful of local tournaments, regularly play at your local clubs/gatherings (which doesn't mean every week, but as often as possible) and "show the flag" while enjoying yourself then you will get people coming to play - just a few...but it feels good when they do!
I recently had 2 guys here ask me for a game who'd been playing FoG for ages & hadn't played DBMM since the playtest versions.... they "now" prefer DBMM, having played FoG because most of the 15mm players adopted it......
DBMM is primarily 25mm here....but because of this guy & a couple of others, plus people with armies in both scales, we might have 6-8 people able to play 15mm locally - about as many as 25mm (some play both).
DBMM is picking up here - slowly - and it doesn't matter how few games I play I plan to enjoy all of them!
So IMO forget about how many people play other rules - they are not important - be good to the people who do play DBMM - cater for what they want as far as possible,
and let the gospel ring out the truth....er.....I mean - just enjoy what you have