I'm glad they did it. No, they'll never bring it back.
Technology goes forward and if this is no good for you, get the old, thick Macbook Pro and you'll have your old ethernet with no adaptor.
There's no miracle.
The rMBP is thick enough to have a minimal ethernet port on it, but it would not have been as "pretty" as the line of ports that they currently have. The only reason they don't is because they don't need too; people willing to pay for the rMBP will pay for the ethernet adapter if they need it, and they will use wireless when they do not need it.
Ethernet is very far from a dead technology. It is kind of unfortunate that it has such a large head though.
I own a 15", 2011 MBP, and I love it, but I am thankful that I have all of my precious ports. The problem with using an adapter is that it removes the given port for use for something else. Not to mention, $30 for a USB to Ethernet adapter
will slow down a fast ethernet connection (gigabit), and it's a ridiculous price.
Now, with all of that said, I do look forward to expanded use of Thunderbolt on monitors. I am waiting for the next generation of monitor technology to kick in (4K TVs and high DPI tablets/laptops currently skipping the love for desktop monitors) before diving in, but I look forward to using a monitor like the Apple 27" one that has everything connected to it rather than requiring a separate dock for laptops. Though, I have read that there are consistent problems with using Apple's monitor on a PC, so I hope someone else jumps on the Thunderbolt monitor + dock bandwagon.