My opinion is my opinion and no one else's.
While this may seem like a good idea, I do think it's best if it stays an LTM for the following reasons:
1. Making it standalone will make it less special. All of Monolith is united for a week for this event, making it permanent will give mono one less thing to look forward to.
2. Staffing Issues. Creating this as a standalone server will require one of two things: Giving all current staff privileges on the new server or getting new staff. Staff would be more likely to pick one server and stay with it, which could hurt the other server more.
3. Development. Someone is going to have to develop the game mode further. Keeping it in it's current state, it would die very quickly. It needs someone to update it in the same way that monolith gets updated. Who is going to do that? Are more developers going to be hired? Are we going to use our current development team? If it's the latter, then less development time will go into monolith, which may result in it dying off and an even more unhappy player base.
4. Player base. Given the fact that Monolith has been on a downhill slope for the past couple of months (in terms of player count), I don't think it's a good idea to split the existing player base in half, as others have mentioned in the replies as well.
5. Cost. I don't have access to Thriving Venture's financials, but the cost of running an additional server, paying developers, and actively maintaining a community is probably not something to be reckoned with. One might argue that it would pay for itself, but ultimately, more players would have to buy into it. Would it be fair to give a player premium benefits on both regular mono and the HL2 server? How are you going to convince someone to pay for premium on both? Are you going to make them chose between one or the other, splitting the player base even more?
Look, I haven't had the chance to play the event yet, but from what I have observed during staff sits and monitoring the server, everyone seems to be enjoying it. However, traditional Monolith and a HL2 rp server can simply not coexist right now from the way I see things. One of them will suffer. Either standard monolith will decline more or the new HL2 server will struggle to get off the ground.