Things aren't clear right now because neither Roblox nor Tallarico have commented on the removal of the sound effect, but it appears to be gone for good.

Roblox, the somehow-increasingly-popular free video game, is ready to monetize its newfound infamy. The game’s oft-memed death sound — a strange and comical "oof" — will now cost in-game ...

The sound effect is hugely popular, and is well known in and out of the Roblox community - it has been used in countless memes and videos around the world.