Keep the email accounts connected for a good reputation. There is no such thing as just "warming up" anymore.
There is a common misperception in the market saying you just need to "warm up your accounts". This is not correct. Just having to "warm up" an email account is a misperception from email marketing. Your true goal is not to warm up an email but to bring the email to a natural state by means of a natural overall average response rate. In other words, mailivery is the service that brings your total response rate (your real emails + mailivery emails) to a natural state. As soon as you deactivate mailivery, your response rate goes to abnormal again, and you could land in spam more often, again.
The logic behind it is that an email address with a good reputation as an average response rate of 5% to 10%. Cold outreach emails typically only have a 1% response rate. If mailivery can boost your average response rate, spam filters will categorize you as "normal" emails, and you land in the inbox more often.
If you really just want to warm up an email and want to take the risk to lose the reputation again after, warm for 8 to 15 weeks.