"Dead" - typically means unsupported, so unpopular, not 'cool' etc.
A few people feel because a game isn't "officially" supported anymore it is "dead" and isn't worth investing in. Arguably this is more to do with local gaming scenes and how likely you are to get a game against someone with said system.
However, I know supported systems for which I know no players and unsupported systems for which I know several players. Warmaster, for example, continues to have popularity at my local club, but the likes of Warmachine/Hordes and Malifaux etc haven't been played in the 5+ years I have been involved. Horses for courses.