Q&A for How to Access iMessage on iCloud

No, you will not lose your messages. They are saved to your iCloud, or your Mac may be synced with your phone number.

You can't. Once messages are deleted, they're gone forever. Try another solution.

You can't view iMessages on a PC unless it's a Mac. If it is, sign into the same iCloud account as your iPhone, and iMessage should be pre-installed.

On your iPhone, go to Settings → [Your Name] → iCloud and turn on Messages to sync them to iCloud. On your Windows laptop, download and install iCloud for Windows from the Microsoft Store. Sign in with your Apple ID, check the box for Messages, and choose Sync. Messages will appear in a new iCloud folder in your Windows File Explorer, but they are stored in a database file, not easily readable. To view them, you'll need a third-party iCloud Messages extractor/viewer tool (like iMazing, iExplorer, or CopyTrans).

Yes, but not simultaneously in the Messages app. You can only be actively signed into one Apple ID at a time in the Messages app on a Mac. However, you can: Switch between accounts by signing out of one and into the other in Messages → Settings → iMessage, or Use separate user accounts on your Mac (System Settings → Users & Groups) for a true separation, logging into each with a different Apple ID.