You deserve every penny they paid you

Value yourself more.  Don't wait for others to value you.

You seem to care a lot how others see you.  You are giving others too much power over you.

You have a need for an external focus, like a project you are working on, in order to feel secure, because only then, you can be value to others.  While growing up, did your parents only give approval when they saw you working?

Valuing yourself entails taking responsibility for yourself, which requires that you know where your responsibility ends and other's starts.  Focus on your side of the boundary by knowing where the boundary is.

If you were in your coworkers' shoes, someone comes in with a new system that will render your knowledge and skills obsolete, how would you have reacted?

Managers don't like to hear "It's not my fault, someone else is to blame." So if you care about leaving a good impression, just express your understanding of the situation, during the exit interview.

(Your cognitive unconsciousness is crying for that valuation.  Start valuing it.  Don't wait for someone else to do it because no one is coming.  When you no longer feel needy in that regard, your office situation will improve.)