Do I get back all the search engine rankings I had after having blocked a domain using robots.txt?

I blocked Google from crawling my domain using a robots.txt rule

User-Agent: * Disallow: / 

by mistake. Just recently I noticed, two months later, and I removed the robots.txt file. The website was previously well ranked for certain queries. Now it is obviously not, with most webpages having disappeared.

Will I take a permanent hit on my rankings because of this? How much time should I expect it will take to recover it? Is there anything I can do to speed up the process?