I'm glad you brought up the Player Participation Policy...
"Personal reasons" (births, deaths, etc) are a documented exception [Sec I. B (3)] in the policy (link:
https://pr.nba.com/wp-content/uploads/sites/46/2023/09/NBA-Player-Participation-Policy.pdf), so there really is no reason for the Spurs to play any kind of games to avoid consequences of the Participation Policy.
There is some wording in the policy that an injury is "bona fide" if the player misses the game immediately preceding or following the National TV game [Sec I. B (1)], so if the Spurs wanted to have Wemby miss the XMas game, it does help if he also missed the game tomorrow... but again, Person Reasons is already specifically exempted, so there is no reason for them to do this.
My not-so-far-fetched conspiracy theory is that Wemby flew to France and it is open ended on when he'll return. Maybe it will be in time for the game tomorrow, maybe not. Maybe he'll return tomorrow but be jet lagged and they'll just sit him. Or maybe he'll play. Or maybe he'll decide to spend more time in France and not even be available for the Christmas game. And for whatever reason the team and Wemby decided they don't want people to know.
Or... maybe this is just legit load management.
Either way, if it is NOT truly injury related, then fans lose by the team simply not being more forthcoming. No one is going to to hold it against Wemby if he's going to his grandmother's funeral. But there are likely people buying tickets they might not otherwise (or at a higher price than) if Wemby were not playing. I just wish the Spurs treated fans (customers) with a little more respect.