Steering racks can leak for a while before needing to be replaced. Your rack may leak past 300K miles and still be in service albeit leaving a few drops on your garage floor and needing to be topped off with PS fluid from time to time.
If you are in a hurry to lighten your wallet by $1000 then by all means be mad and find another dealer to install a new rack ASAP.
However I wouldn't be too hard on the current dealership...the tech was just doing his job by noting what he is supposed to note. The adviser is doing his job by keeping your truck safe and helping you prioritize your repair dollars.
There are also degrees of leaking, everything in between "the seal was wet" to "there was a puddle on the floor". Just because a leak is starting doesn't mean you need to drop everything and replace the part. The leak will get worse and at some point the rack will need to be replaced. When? depends on how fast the leak progresses.
You aren't be in danger of losing your steering per se; if the system leaked dry you would lose the power assist feature, making it very hard to steer but still doable. If you have strong arms you could guide the truck off of the road but you would not be able to drive it far without power steering (unless it was a straight road with no turns LOL).
Likely you will notice the leak on the garage floor loooong before you lose enough PS fluid to lose power assist. Seeing as you can buy PS fluid in almost every gas station and parts store, topping it off if necessary will keep it going until you replace it.
I think the dealership is on your side....as far as the cost, a remanufactured AC Delco rack is about $300 at Rock Auto. Sometimes these can be a bear to install depending on how/where they are attached. I don't have rack & pinion steering the burb so don't have a basis for comparison.
Now that you you know that it is starting to leak, keep an eye on the ground for leaks and also on the PS fluid level. When you're topping more than you like to, then it's time to schedule the repair.
Rarely if ever do you see a catastrophic leak on a steering rack where it just dumps the fluid and leaves you stranded. Again, I think your adviser is on your side here. If he wasn't he would have pushed hard to sell you the job as urgent.