It is but that page is also trying to get you to use method 2 which is their software.

Things like Paypal and ebay should be accessible if you have his phone and email access even without the Windows machine. Just hope he saved passwords. If he didn't email+phone should get you there in almost all cases to reset them.

Rebooting the device shouldn't affect cookies and really wiping the user's password is going to be the quickest way.

Also should you get as far as Windows running, to get to things like auto saved passwords in the browser (rather than just resetting them):
https://www.nirsoft.net/utils/web_browser_password.html

To extract an mail password
https://www.nirsoft.net/utils/mailpv.html

Outlook PST password:
https://www.nirsoft.net/utils/pst_password.html

There may be some other useful ones here too:
https://www.nirsoft.net/