Im with you on this one Ant, when I play and see servers alive with home grown maps, this indicates to me it still lives on.
The fact that it seems to have been less active a community than in the past, shows that people's lives change and priorities change, they may still map/play for HL, I myself have set priorities and enjoy mapping for HL1, CS and CZ. Alot of my maps are not published on the Internet, they are played at local LAN gaming sessions in my area.
I cannot devote a full week or month to any one map, but instead I spend about 3 hours every second or third evening, a map can take me anywhere between 60-140 hours to complete and that could elate to 2-3 months.
So I believe that HL will not die, it may give that appearance at times but I find it alive and well here in Australia (kinda like a secret clan thing), my only advice to others who may see HL as dying, is to keep your interests/hobbies alive, sure it takes good time management but its worth it for me.
I don?t need convincing wether its dead or alive, that is evident from good site's such as TWHL or Snark-Pit and the helpful communities within them, Sure some people have bad attitude and flame your map's that you submit, its water off a ducks back to me, I don?t get offended easily, if people act childish and make negative remarks, it's either jealousy or maybe because they are children or the fact that some people cant handle criticism.
I like mapping because it gives me a pallet to express my fantasies of fictional worlds/places.
The only time it will die is when power supplies for our electrical equipment diminishes/ends.....but I will be long gone by then
(just my 2 cents worth)