I am worried of this happening. So I keep spreadsheets concerning DNA matches. In which case I have the important details I can use if they happen to disappear from my matches.
I record the name of the match, age and location, if available, either name of parents/grandparents or line to common ancestry if known, and the shared cM.
For those I find a shared line I add a note to the child of the shared ancestor (that is my ancestor) and add a ⚕ in the title of their name. So I can see which lines are DNA proved.
