No I do not think that Amanda Bynes will ever again be a successful actress. Actors and actresses do not get many chances to stay in the limelight and continue to land successful roles. It especially does not help ones career to be doing things that put them in a negative light.
Sadly, Amanda Bynes has done somewhat of a tailspin, and seems to have a lot of personal demons. In addition, she has insulted a lot of other people in the entertainment industry. It's doubtful people would be willing to accept her back into acting again. That being said, it's always possible if she really wants to make a change. People like comeback stories. But it would take her really realizing there's a problem and working her way back up to the top. So, because I don't see her making these necessary changes, I would say it's not likely to happen.
I've never been a fan of Amanda Bynes not even back in the day when Nickelodeon put here on. She's annoying to be honest and she's terrible at acting. She may have her place in the spot light every now and then, but I don't think she deserves a career in the entertainment industry. The talent isn't there. It never has been.
I dont think she has been successful for quite some time now. People who get in trouble all the time and that aren't currently staring in lead roles constantly, tend to really get the proverbial boot from hollywood. You can't really film when the actors or actresses are in jail or in court all the time.