Is it possible to just copy and paste the wiki page library from Sharepoint 2007 on premise to Sharepoint Online 365?
It is not good idea to copy and paste the Wiki pages from 2007 to office 365. You better use migrations tools to migrate the pages so that content also will migrate as expected.
You can use Share gate free trail to move the wiki pages. here is the link to download the setup file and you need to provide correct email(it won't accept gmail or yahoo mail) so that you will get the license https://en.share-gate.com/download
Full disclosure, I work for Sharegate :) I can confirm that no, we do not delete anything once the Free Trial ends!