I have some rhubarb seeds hidden away from at least that long ago!! I would try them, what's the worst that could happen? The hardest part will be waiting for them to germinate (for me it takes foreeeeeeeever).
I've certainly been sowing rhubarb seeds from the same package for consecutive years without a problem, so they're not the most short lived seeds.
I don't remember germination being slow either. More of a problem - for less than patient people - can be the slow development towards mature plants. Having to wait 3 years for your first harvest is a long time, although some varieties can start giving some yield in their second year, but you can't take too many stalks from a juvenile rhubarb plant.
Then there are the genetic variations between rhubarb plants grown from seed, which is also a big reason why rhubarb gets cloned a lot, because then you know what you get. If you do sow rhubarb, it is advisable to let quite a few seedlings develop, then later select the best ones. I've grown a few different varieties of rhubarb from seed, it's interesting and not difficult, but it takes a bit of devotion.