Note that missions appear to have a 4 days lifetime. If you don't take them, they go away. I had a rare mission for a bonus raid roll pop on friday afternoon; it was there this morning and gone when I came back from work (I'm EU, maintenance is tomorrow so it's not that). Ditto the 100 GR mission that popped at the same time, and the 615 necklace. The follower token mission that popped the next day is still there.
Hint: if you have things that are worth it, but don't have the followers to guarantee your mission success, send your best effort before the 4 days elapse or lose the reward (the Mission Planner add-on will make the best chance % composition for you).