Can I watch the courses that i have already passed if I stop paying the full subscription?
Noooooooooooooooooooo, you cannot
Really, even if you already have the degree?
With a subscription you are paying for temporary access. If you want permanent access, you need to outright buy the courses. Otherwise everyone can rush through all the courses in a month and get certifications and have access to all courses. The certification is moot.
…a purchase by prepayment for a certain number of regular deliveries of something (such as issues of a periodical) or for a certain period of access to or use of something (such as an online service)
Although they officially say you can download any course that you watched during your subscription so for what it is worth you can do that…