I crossed paths with two TBM's earlier today. Both were in tears over this lovely man's passing. I would expect much more of that this Sunday. I won't be there to verify any of this.
Hell, yes. It will be testimony meeting for 99% of them (a few may have a ward or stake conference). testimonies as to the goodness of President Monson will likely dominate most of the meetings.
Not only will they mention it, they will have the chance to mention it on Fast Sunday. Everyone and their 12 kids is going to file up to the stand to mourn the loss of the Beloved Leader. It'll be like a North Korean funeral service...
Fast and testimony meeting is typically the first Sunday in a month except when conference(general, stake, or ward,) moves it to the week before. This IS the first Sunday of the month. It will be Fast & Tedtimoney meeting for the vast majority of Mormons.