There's no way to know for sure unless you collect info from the SOURCE. Put on your best "programmer" outfit and infiltrate Game Freak HQ incognito. Locate the Pokemon GO planning room and scavenge for information. Hold Masuda hostage if you must. Do not waver from your purpose. With enough willpower, you'll indubitably figure out - once and for all - whether Suicune is ever coming back to Pokemon GO raids.
Hope this helps!
