Just to clarify, different versions of Half Life 1 have different DRM:-

Half Life (original retail disc) = DRM'd. Can be NoCD'd

Half Life (GOTY retail disc) = DRM-Free.

Half Life (Steam) = DRM'd. Works with Goldberg though.

Half Life Source (HL1 in HL2 Source Engine) = DRM-Free.

Black Mesa = Unofficial "reimagining" of HL1 in the Source Engine. Linux version is DRM-Free.

Half Life 2 (inc Ep 1 & 2) = DRM-Free.

Portal 1 = DRM-Free

Portal 2 = DRM'd. Works with Goldberg though.

As for coming to GOG (or any store that isn't Steam), it's highly unlikely for tribal storefront p*ssing contest reasons that have nothing to do with DRM...