do i lost data in roll back table conversion?

hi my friends.

i have a serious problem in adjusting a z table in se14.

i change the type of a field from chr to num .

but i got this error : "adjustment terminated in step 5"

i search and find this link :

how to roll back table conversion? - Technology Troubleshooting Guide - SCN Wiki

now i have a question : if i do rool back table , do i lost all of the data ?

i have  big and  really important data in my table.

please help me.

thanks.