Warman is its own municipality with its own Board of Revision, distinct from the City of Saskatoon, so a sale price there feeds the next assessment cycle rather than adjusting the current one. A house that sells for less than its assessed value can carry that same assessment, and the same tax bill, until the town's next scheduled reassessment.
If a recent sale genuinely shows your assessment is out of line with the market, that comparable sale is exactly the kind of evidence a Board of Revision appeal wants, but the appeal has to be filed within roughly 30 days of the notice date rather than assumed to happen on its own.
A seller weighing whether a lower price is worth it should separate the sale decision from the tax question entirely, since one does not fix the other automatically. Get your hand-reviewed valuation from Joel Dyck.