We have been there many times (8, I think). The last rip was the year before the storm. Most trips have been in January though the last time was in early June. There was no material evidence of sargassum in the anchorages though there were a number of patches of it offshore that we tried to dodge when motoring and had no problems.
From St. Vincent, the only options are Barefoot Yachts, and Horizon, Typically the boats available are several years old though Barefoot has been bringing in some new boats periodically and they show a Leopard 50 on their web site. Both are relatively small operations (as compared to the BVI) with about 10 boats each.
We have used Barefoot 6 times and Sunsail for 2 trips as they used to have a base there. Barefoot does a good job.
I have no information regarding Mayreau though I imagine the Righteous and Dennis are back in business. I suggest you talk with the charter company of look at other web sites for current informatio.