You can let it go above 70, you just probably won't like the result. I use 320, but keep it between 62-64 in a fermentation chamber (keezer). I'm not saying it won't be drinkable, just that you may get off flavors you aren't wanting.
Offhand I can't think of a wheat yeast that does well above 70, unless your specifically trying to get more banana/clove character. If you just want a clean beer, throw some US-05 or Nottingham in.
You may have to sanitize a long handled spoon and rouse the yeast (320) but be careful, and you may wake it up by getting it in suspension.
Kegged: Feast of Fools (Braggot), Drunken Punkin Dunkel, Raspberry Wheat, Chocolate Cherry Porter, Oktoberfestive ale, Apfelwien, Rochefort 8 Clone, Centennial Blonde, La Fin Du Pistoles, Surly Furious, Ryed On Saison, Celebrationizator Dopplebock, Ryebock, Lemon-Lime Hefe, Chamomile Honey Wheat, Blue Ridge Moon Wit, Patersbier,
Primary: Bourbon Vanilla Imperial Porter, Cherry Brett Saison, Imperial Irish Red
Secondary: Gulden Draak, Peaches & Cream Belgian Tripel