I think you mean the only way you can get Netflix is if you 'upgrade' your firmware. If so, then you are correct as far as I know. I know a while back Netflix was sending out free PS3 Netflix discs, which is where I got mine. The only thing is, you have to pop the disc in every time you want to use Netflix. Kinda gets to be a pain in the ass. But yea, I'm not sure if they're still handing these out or not. You might want to look into that.
But other than that, yes, you'd have to upgrade to get the 'discless' version of it. It IS very handy but... Once you upgrade, there's no going back. From that point on, your ps3 is in Sony's hands and your system will get further raped of it's features. I wouldn't reccomend updating but if you feel you desire discless Netflix that bad, then by all means go for it.
As far as getting rid of the jailbreak, all you'd really have to do is delete all the homebrew you've got, games, etc... Then just never jailbreak it again, it's that simple.
my guess is any one who has the disk it will be a coaster real soon if not already, so there would be no since in replicating from the disk our only hope is a JB payload that works on FW 3.42 and allows PSN sign in as those are the new requirements of Netflix diskless.
I have the disc version and they are deactivating the usage of the disc. You can only access it with the app after 9 days from now (in my case) I hope a workaround comes out. You can download the app as a pkg file and easily install it but it doesn't work.