As far as the organisers are concerned, there is no reason to change the basho in any way just because one of their headliners has tested positive - this means continuing with the planned cap of 5000 spectators, distancing is respected and no cheering (to minimise spray). Unless the federal or prefectural government steps in and asks the sports associations to specifically change something, they will be going ahead as planned. The last basho had an entire stable unable to participate because of an outbreak that happened right before the start, and they continued as planned back then too.
The sports associations are under tremendous pressure right now to prove that they can still operate safely with the current situation because of the upcoming Olympics. If they’re unable to manage a sumo tournament, then the Olympics will definitely be an issue - And that would mean a lot of lost revenue, and even more hardship for communities and small businesses that have already made a huge investment in preparing for the Olympics. So it may seem like just a basho now, but it adds up to something much bigger later in the year.