A: There is no way to know if your leads have signed up for the webinar, the leads are the handled by John and there is a follow-up marketing campaign sent out, through which they can make a purchase.
When someone clicks your hop link, a cookie is placed on their browser.
As long as the customer does not click another user's hop link, clear their browser or change devices/browsers, you will be credited with the sale.
The cookie is valid for 60 days.
Alternatively, you can set up an opt in page / form, where you collect the emails before sending the leads to the webinar sign up page, to collect their emails and market to them directly later, yourself.