Yes, you can fail declarations, but from what I've noticed, it tends to be the exception rather than a rule.
Even if you're forced to spend fate points for the ritual, each fate point is going toward a definite +2 on top of a definite 4, whereas a Mortal's invoke on a Contacts roll is a +2 to anything from a 0 to an 8, unless you're using it for a re-roll. If you want to be certain that a Contacts roll is going to make 8 from a start at 4, you're probably going to end up blowing at least three fate points to account for rolling a -1 or -2 on the dice--and that's if you have that many applicable aspects to invoke.
There is, yes, the chance of failing a casting roll, but that risk comes against the certainty that once you have those 8 shifts ready, you're going to end up with an 8-shift result. Plus, you get to set the difficulty of each roll. Unless you're in a dire hurry, there's nothing stopping the wizard from making 8 1-shift rolls to meet the difficulty.