Lichess went down and I lost 2 ½ minutes time and lost on time. I was up material. How can I get my rating back? This isn't a fair way to lose.
https://lichess.org/faq#disconnection-loss
Unfortunately, the only way for you to regain your lost rating is through playing. While that might seem unfair, I'm assuming that it would be extremely impractical for lichess to search every game that was ongoing after a server outage, make a judgement call for each one, and refund rating points.