Janeway wasn't the type of captain to quit and not try. From the very beginning, she said that they would be looking for ways to shorten their voyage home via wormholes and new technologies. So a 70-year voyage wasn't really an option for Janeway.The thing that put me off of Star Trek Voyager from the beginning (among other things) was the whole "70 years to get home" and Janeway's constant prattling about "getting the family home".
If it was really going to take 70 years to get the ship back home........then there was no point in trying anyway. There was no reasonable way the ship completely unsupported was going to go on for 70 years.
That tenacity is what separates Janeway from a more timid captain who would have just given up.