TT is, despite being digital and at a distance, personal. You LIKE the person’s videos and decide to subscribe.
To the viewer, the fact that your buddy is giving you the account is not much different than if some hacker took over the account and said, “Hey! Same username, so you and I is friends!”
Not going to happen.
And, it will kill your brand before you even get going.
Approach it from a slightly different angle–post a few of your videos, and then have your friend do some duets or testimonials of your material, and explain he is leaving the industry, but his fans may want to check you out.
Yes, you will lose most of them–but you will also start with some of them.