What do you mean by comeback? Outsell or match PlayStation in sales like with the Xbox 360? Or have a decent selling console, but still falls short of the competition like the Xbox One? 

Microsoft would need to sell a console with similar power to PS6 but at $100 cheaper and have every first-party game exclusive to have a shot of outselling PS6 with Sony making more blunders.

Now to have a comeback in which they sell 50 million to 60 million with Helix? Sure that is possible. But they would need to:

• All single-player focused 1st-party games be Xbox/PC only (Yes, including Elder Scrolls and Fallout)
• Classic Xbox IPs Xbox/PC only - Halo, Gears, Forza, Fable, etc
• Disc drive add-on
• Have 2 SKUs, but more like PS5 and PS5 Pro, rather than Series X and S
• Console price needs to be more competitive than what we see now
• Better marketing
• Market that they own Call of Duty, even if they can't make it exclusive due to deals in place
• Bring back limited edition themed consoles
• Bonus:
  
  • Better name - Xbox 7 and Xbox 7 X (Here is how I came up with Xbox 7 - 1. XB, 2. X360, 3. X1, 4. X1X, 5. XSS, 6 XSX)
  • Port World of Warcraft to Xbox

I really don't see Xbox hardware being able to avoid a continual decline before eventually outright dying at some point. They'd need to do something as drastic as going so hard on exclusivity again that they stop releasing PC versions of their games to even have a shot at stopping the decline but that would kill software sales and the long term popularity of those IPs so I highly doubt that'll happen.

People have built up such large digital libraries in the ecosystem they're in that platform switching will be rarer than before and young gamers won't be choosing Xbox much currently so the average Xbox user is probably getting older every year at this point. That's also the case for Playstation I imagine due to young people being less into consoles nowadays but they've become the default home console choice so they're in a way better position.

Is there an opening for them to regain significant marketshare and cred? Technically yes; grab a PR win by continuing physical discs, pursue exclusivity, price Helix aggressively even if it means eating substantial losses.

Will they capitalise on it though? Most likely no, the last 13 years tells us they consistently fumble opportunities like this by shooting themselves in the dick repeatedly.