you're talking about your rogue already being detected and being swarmed by enough enemies so that he can't use evade or stealth to get out of the way, that sounds like a fault on your own tactics. Why are you standing toe to toe with enemies in the first place? You are a rogue and what do rogues do? They do it from behind, where the sun don't shine. If you're charging in before the warrior taunts or challenges a opponent and start trying to melee them you're doing it wrong.
Does this mean no rogue can ever initiate combat? No that's not what im saying, but there is a time and place for everything, and if the enemy is one of those types that isn't going down in two hits or you don't have skills that can get you in and out of melee fast, then don't do melee until the Warrior has pulled aggro.
Flank attack is probably the go to attack if you aren't sure how to play the melee rogue in DA:I, if you evolved it it automatically stealths you after the two hit combo which allows you to get out of melee range most of the time, timing aside the enemy will usually have to turn to face you if it notices you at all. (There are passive stealth abilities that reduce threat for simply having them and this mean sometimes enemies will outright ignore you if they lose track of you, hence Flank attack's auto stealth)
Flank attack is also instantaneous teleportation behind or through a target, if you see a creaturing going to attack you and you have it ready or you don't think evade is a option, use flank attack. If you are really desperate, Flank Attack then follow up with Evade (assuming you evade through an opening) you should have no one on you at that point as flank attack stealthed you, evade left a decoy and reduced threat.
Here's a turn by turn for most of my adventures as a Melee Rogue.
1.) Stealth when approaching unaware enemies.
2.) Use Spinning Blades on unsuspecting enemy.
3.) Use Evade to get back out of range OR use Flank Attack if enough stamina is available to gain stealth again and walk away if target hasn't been challenged or taunted.
Wash and Repeat as necessary. I thought i had a video of one of my game plays as my melee rogue on my PC i was going to upload it, but apparently i didn't record it. However I'm willing to do this if it's necessary.