You have until the next level increase to max out your destinies, why rush? Everyone who maxes all ED than complains they have all the loot and all the ED they are bored and leaving the game. Or you can have you main destiny and all your twists ready for the next quests to come out. It is up to you how much you want the fate points and how fast you want them. Just like a completionist. There are pros and cons to both.
Some people don't even have the ED pack, so you losing your main destiny while leveling another doesn't make your char unplayable. You can pick and choose which content and which diff you play while in gimp status. I plan to knock out most of my levels before even getting into my main on my first Epic char(Druid). Basically I am unlocking my specific twists first then grinding to my ED. This seemed easier to me by using lower quest levels and EN/EH to get thru the EDs that don't match my char so by the time I am hitting EE and harder quests, I am in my main.