You can keep your site active as long as you want. Most clients leave it up for one to two weeks post-event.
To redirect visitors once your site is no longer active, go to Site Settings>>Redirect and enter the website address. Clients typically reroute traffic to their organization's website.
For live stream virtual events, your site will be in livestream mode for the period of time you specify, but as will other types of events, your Swell site will remain active as long as you would like.