The only changes that happened to the Resource Instance spaces in the latest patch was the inclusion of the new entry restrictions/timers. None of the gameplay inside the spaces have changed, nor have the monsters received a boost in difficulty. They are the same as they were previously.
Also, you are able to enter and exit those instances at will as frequently as you want as long as you have the appropriate "Kill Boss" quest active in your journal. Once that quest either fails due to expiration of the timer or completes upon turn in to the appropriate NPC, you will be barred access. Failure incurs a 2-hour retry timer on the quest. All of these changes were detailed in the patch notes.
If you need to bail from the instance - due to either a bad pull or a bugged AI keeping you in combat, the only cost you'll incur is the time you took to run out and back in (the timer counts down regardless of being in the instance and regardless of whether or not you are online).
In a perfect world, you wouldn't have to worry about the AI bugging out in those spaces. We're investigating that but a fix for that specific issue likely won't occur until Book 8 at the earliest.