Is reach dead?
No.
If the matchmaking is still being played, then no.
No, not as much people are playing the game right now. It's still active, but a small amount.
Nah it’s still alive, just waiting (Painfully) for my H:Reach Limited Edition to arrive so I can play it again
Ok Jesus only asked a question
Depends on your definition of dead. The population is woefully small (to be expected the game is over 8 years old), but there is a population.
Is reach dead?
There's also an Xbox game night group out there. It's been awhile, I'm unsure if this group is available through the 360, but install the game on the Xbox one and the link is available.

Cheers,
Brad
In terms its not as populated as it was in 2010-2013 many moved onto other halo games but there are still those who play halo reach to this day.
It’s not dead, but it would be a lot more populated if the servers weren’t so awful. Regardless, it still maintains a steady 3-6000 players whenever I go online.
It'd be cool if they remastered the game.
The PLANET of Reach is destroyed, yes, but not the GAME, Halo Reach.