If my disaffiliate you mean withdraw then yes you can come back.
If you read the national policy handbook you are alum if you 1) graduate 2)leave the college or university in good standing financially. participating in order of the triangle is not required.
Also-- except for expulsion if you are fiancially expelled you may be reinstated as an alum if you pay your outstanding debts and its been 3 years since your expulsion.
also-- if you withdrew your membership you may petition National COuncil and prove you care about SK and want to be a good alumna and they can reinstate you. Only explusion is permanetly severing your ties.
I have helped 3 alums who b/c of financial and family hardships had to withdraw in college become SK's again. They still kept in touch with sisters, donateed to their chapter's events as alums (time and money) and had other SK's write letters on their behalf stating they cared about SK and woud be great members but circumstances lead to the having to wthdraw as collegians.
PLease get the terminology right though. You are not: disafilliating or deactivating but either active, alum, or you withdraw