Well, Sinner has a 3 month ban, but it ends before the Rome Master's, and he'll be able to play the French Open.  Honestly, it seems a little weak from WADA.

During this time last year, he accumulated 1900 points, so he'll go down to 9930.  He was absent for most of the early clay season, so that's why it's not really affecting him that much.  Can anyone take the #1 ranking from him during that time?

Zverev and Alcaraz are the only credible contenders for that.

Removing their points for this period from both of them leaves Zverev with 7185 and Alcaraz with 6010.  Indian Wells, Miami, Monte Carlo, and Madrid are on the schedule, so it is theoretically possible for either of them.  Djokovic in 2011 pulled off 4 Master's wins (Rome over Monte Carlo in that list), but I'm not seeing either of them pull that off.

Zverev is playing Rio and Alcapulco, so he can gain up to 1000 points there.  If he wins one of those tournaments and does very well in the Master's, then he's got a good chance to take over the number one ranking.  Whether that would be a good thing or just cause him a huge amount of stress for the French Open is another question.

Alcaraz probably needs to run the table on all four Master's.  Alcaraz didn't play Monte Carlo last year.  He also didn't play much clay since he was injured a lot.  I think it's a question on whether he'll pack his schedule or not, with my personal feeling being that he'd lean to "not".