Does the tracking link persist?

Okay so here are my 2 cents:

Case 1.

assuming you have a query param in tracking link www.test.com?cmp=mycampaign and you ensure to track query param "cmp" value in eVar1 (expire on a purchase, allocation last touch) and full tracking URL eVar2 (expire on a purchase, allocation last touch).

When the user lands on the site through this tracking url, campaign value 'mycampaign" is captured in eVar1 and full tracking URL in eVar2. If a user exit to another site or non-adobe tag manager tracked page/form in purchase flow, an exit links tracking gets fires out of the box through the Adobe tool settings.

In this case, when a user comes back to the site and made a purchase (lands on Thankyou page), Adobe treats it as a new entry, but don't worry as we have already captured campaign value and URL in eVar you will see eVar1=mycampiaign, eVar2=www.test.com?cmp=mycampaign.

Note: eVar expiration setting will impact the desired outcome.

Case2. 

assuming you do not track query param value in eVar1 and URL in eVar2.

When the user lands on the site through this tracking url, full referer link will be tracked as "www.test.com?test-url. If a user exit to another site or non-adobe tag manager tracked page/form in purchase flow, an exit links tracking gets fires out of the box through the Adobe tool settings.

In this case, when a user comes back to the site and made a purchase (lands on ThankYou page), Adobe treats it as a direct entry page, there will be no referrer link and the user purchase will be treated as a direct entry purchase.