No! Only the campaign is deleted. All the leads remain in the system
For example:
Initially, there are 101 leads in this workspace

Out of which 100 are in a campaign

Now lets delete the campaign


But all 101 leads are still present in the system

No! Only the campaign is deleted. All the leads remain in the system
For example:
Initially, there are 101 leads in this workspace
Out of which 100 are in a campaign
Now lets delete the campaign
But all 101 leads are still present in the system