" have not lost any information on laptop. I thought that when motherboard goes all is lost."
No. If you exchange a like for like, then the hard drive will see no difference. The only thing visible or different may be the bios version. The newer motherboard will probably have a newer bios.
" Could it just have been repaired and I paid more than I should?"
That is possible but would be the kiss of death to the company who has charged for a new motherboard and not supplied it. If it was proven then the internet can quickly spread the outcome and seriously damage a company's reputation.
It should be possible to tell if you have a new motherboard, check the external connections, usb, vga,firewire etc. They should all look shiny new and be no play when you plug in a connection.