Halo: Reach Availability – Offline Play, Xbox Live, and PC
Halo Reach is not exclusively on Xbox Live.
Here's why:
Halo Reach is a standalone game: You can buy it on disc or digitally, and then play it offline.
Xbox Live is required for online multiplayer: You need an Xbox Live account to play with friends online or participate in matchmaking.
Halo Reach is available on PC: However, it's not through the standard Xbox Live service. It's part of the "Master Chief Collection" which is available on Steam and the Microsoft Store.
In short:
You can play Halo Reach offline.
You need Xbox Live (or a PC account) to play online.