Can I get my messages from an old number to another without having acces to 1st

Hello,

I had WhatsApp verified on an old phone number. I've lost acces to that number and I can't get it back. But I don't want to lose my conversations.
First, can someone else get the phone number and verify it?
Second and more importantly, if I get another phone number, then verify that one on the same device, can I still see my conversations? Or do I lose them? Are the messages stored on the device? I did make back-ups, will I be able to restore my messages from that backup if the phone number is different?