Moved this to a better section where you will likely get more responses.
Short answer - you are probably going to lose the views and maybe subscribers who come to your channel for Roblox videos. And since you have a lot of videos of Roblox, you will continue to rank in search for Roblox videos. That means someone will come to your channel via a Roblox search, see you aren't doing Roblox and leave.
So yes, it is going to take time to pivot. You will need to determine how much of your current audience cares about Minecraft. That will take some time. Then you will need enough content that your Minecraft stuff ranks in search and discovery, etc.