timestamp variable type losing data

I hope I can explain this so it is understandable. I have an object within
a table which has a variable type of 'timestamp'. This is the close_date
for an in-house ticketing system. It has a relation to another table which
has the listing of all of the administrators. The problem is that if one of
the administrators leaves to go to another job and then we remove them, the
timestamp value associated with all of the tickets that this admin has
closed loses it's value. So, now we don't know when the tickets or tasks
were completed from the past. I tried re-adding the admin but the
timestamps do not return. I figure we probably lost the data, but I don't
really want to lose it again. Has anyone come across this problem? Does
anyone have any idea as to how to correct it?

Thank you,
David M. Fetter 503.450.6609
UNIX System Analyst
Emery World Wide

"It has become appallingly clear that our technology has surpassed our
humanity." - Albert Einstein