If I sign up for Citi priority pass now and I cancel my card next year, would my pass still be valid next year?

Short answer: No. The priority pass is a benefit associated with the card so cancelling it means cancelling the priority pass.

Long answer: Still no but it also depends on the validity of the priority pass, which goes by calendar year. I believe Elijah has provided a hack to it so you can use it to your advantage.

Cheers

Do note, (mini hack!) Citi's PM priority pass works on a calendar year basis. So if you got your priority pass now with a validity till Nov 2020, flew off in December 2019, used it twice, cancelled your Citi PM in June 2020, then flew in July 2020, your priority pass should still be valid for use. So that's 4 uses for a single year of validity.