lou, you can either replace the tip with a larger diameter replacement (just cut flush if broken uneven and purchase a tip that fits) depending on the fit you can use ferrel cement (super hot glue) or CA (super glue) if the fit is snug... place it on the tip first and mark it for line up before you glue it on permanently...
the ferrel cement approach will give you a better chance of getting it on straight... if you mess up you can heat the tip to adjust it..
CA is a one shot deal..
if you've lost too much tip, possibly you can purchase that half of the rod if it's a two piece rod... one could probably buy the whole rod for the price of the replacement half though...
Beware the "sneak attack"!!