I used to sneak into the music school and get kicked out too! Eventually got a digital piano with a hammer action because I wanted to practice without restriction, never quite the same as playing the real thing but can be a good practice tool if you have neighbours. Make sure you play it first before buying, and they can plummet in value after buying so may be worth looking at second hand.
As for taking back your skills, they are never really lost but they become rusty. If you learnt any pieces of by heart try closing your eyes and play without thinking about what your fingers are doing and just listen to yourself. There will still be gaps at first but you will be back to your standard in no time.
