If your fan is still working, don't worry about it for now. It just means you may not want to unplug the CPU fan again. Finding replacement LGA775 boards is getting hard now, and like you said, warranty probably won't cover this.
All you can do is be very careful when unplugging the fan if you need to do it again, or just don't unplug the fan again when cleaning the CPU.
Hopefully it will last until it gets to the point where it is time to upgrade to a new CPU and Mobo.