I don't think it's worth replacing just the led. Generally led failure ends up being due to a regulator failure. I mean even when over driven with adequate cooling you're looking at a minimum few thousand of hours of use.
When you mean burned out though does that mean doesn't light? Then you could test the led by connecting a multimeter or 3v battery across the terminals and which should light it up. Which means generally a wiring or regulator problem, definitely still better to buy a new module. Or did your phosphor turn brown and and output significantly diminish? Browning phosphor generally means an overheating problem which means you're likely to burn another led or drop-in. So it may still be better to buy a lower power drop-in.
Either way you can see it's better to buy a drop-in unless you're pretty savvy with working on electronics or want to use this as a learning experience with no guarantee of success. Either way buy a new drop in, whether you buy the regulator or led, in that way you'll get it working. No matter what.