Hello, thank you for your question. Regarding a landing page that allows to make an offer, if a BIN price is not set for a SellerHub domain, Make Offer will be the only option listed there.
However, there are no separate links being generated for this, the option is simply available through the interface of the landing page.
If the DNS no longer points to Spaceship, the landing page will stop working as well. However, the domain will stay listed for sale and can be found through Spaceship and Namecheap search interface. So it will still be available for purchase.
Also, please note that at the moment, SSL certificates are installed only for domains that are pointed to Spaceship nameservers. Domains on custom nameservers will not have our SSL certificates.