@Eagle_Hawks1
When Dengar is under stealth, no enemy can gain stealth. If you don't have Dengar, R2 will give everyone stealth - repeatedly. If that happens, you can't choose your kill order and Chewbacca and Han Solo will go nuts as long you leave them alive. You really need to kill Chewbacca first. Dengar doesn't help you too much with damage, but he's the one that prevents Chewbacca from steal thing. Without Dengar, you don't even get a chance to attack Chewie.
That said, if you play the event over and over again, you'll get times - rare as they might be - where r2 gives stealth early and Chewbacca takes two turns before your toons go, so just as your attacks are coming available Chewie has come out of stealth. The problem with this is that the perfect scenario for being able to attack Chewie is also the scenario in which Chewie does a lot of damage early and r2 gets stealth ready to go again right after you damage Chewie but before you can finish him off ... which allows him to attack more and regain health and protection.
So if you get stealth just right AND you get max damage on all your attacks AND r2's AI doesn't use a second time right when you've got Chewie on the ropes, THEN you can finish off Chewie and make a good attempt at finishing the event.
Maybe all those RNG pieces will come together on your very first attempt. Some people have reported getting Chewy on very few attempts even without Dengar. But when I tried the event the first time it was available I played it for hours without getting the right RNG. I gave up, waited a couple months for the event to come back the second time, had Dengar ready and finished in less than 20 tries (and most of those were ones where I restarted before I even took a turn b/c I'd lost 2 or more toons in the opening volley). Probably took a half hour or a little more, and even before I won I had a couple attempts that were really close because I could kill Chewie. It was obvious that it was going much better for me with Dengar even before the attempt that let me finish.
...so. Yeah. You can finish without Dengar if you get the right RNG. Random means random, so maybe it will even be on your first try. But I and many others tried so many times without success that it's pretty easy to see that your odds of triumph without Dengar are low on a per-attempt basis.
Only you can decide whether you're the type of person who would enjoy playing the same event for 12 hours in a row trying to get it perfect of if you're the kind of person who hates bashing your head against a wall of RNG.
If you're ready without Dengar, you might as well give it shot. You might win the lottery. But I couldn't handle the frustration, and most people have found that it's much better with Dengar than without, so even while you're trying without Dengar, you should probably keep farming him.