peers see the rooms and they choose a room and they connect to that room but after they clicking on the room they got kicked because players in the game...and they can't join in the room but room is not full and they can see that ... so this is not good .. because they must join in available rooms .. and if we have a very big room and all peers join into that... we can not do that .. that is obvious..(if lobby host got disconnect - peers disconnect and reconnect problem - they must return to that room after game end they must disconnect again! and who made the room must be host .. but we can not tell who is the host in game because we tell every body disconnect and reconnect again so maybe who is made the room not be host ! and after game that player is not host !!
You just need to be creative to be able to figure that out. You need a room manager, which you can do yourself, I did it, I call it lobbyhost. Instead of open/close room, let the lobbyhost assign running number to rooms, this way is much easier to maintain a unique room number. In my case I use unix time stamp as the running number.
Leaving and joining room is as normal as it is, if you look at any other MMORPG, such as WOW, TERA they did this as well, notice the loading screen? It's actually a fake screen to download current data of the room, not loading the game locally. Game load locally much faster than they download all current data, that's the truth.
In case of you're design your game in a way that you let players to create room themselves, and set who can join with or without password, set the room peer limit, create unique room name, auto join room, this is extremely doable, in fact the the MP plugin was designed totally for this scenario, which we call peer-to-peer MP.
construct 2 is here for making things easier... not harder !)
It is already much easier for most people than you can imagine. Try the traditional way then, see how it goes. The complexity of MP goes exponentially to the complexity of your game, you need to realize that first!
Don't blame the bow if you can't get a bulls eye.