So I have been doing some up grades to my 88 305 Camaro and one of them was a high flow edelbrock intake manifold. After I got everything all back together and running I looked at my old intake manifold and realized that I forgot to take the oil splash guard off of it and put it on the new manifold. So my question is just how necessary is it and will everything still be ok with out it?

It will be fine, you have nothing to worry about.

The splash shield is there to keep oil from baking onto the hot underside (heat riser passage or EGR in some cases) and then falling down again.

True, but I've never heard of anyone having a problem without it. Aftermarket intakes never have them, or the provisions to mount the factory one, and no one ever has issues.

That's because those aftermarket manifolds don't have heat risers. The underside simply doesn't get hot.

Most aftermarket dual plane and some single plane intakes have the exhaust crossover, even if they don't have EGR or hot air choke provisions. My Holley 300-36 has a fully functional crossover, as did my Torker. I think the only intake I had that didn't was my RPM Air Gap. The regular RPM does though. The 300-36 is almost an exact reproduction of the intake GM made for the 302 and LT1 engines, and it has all the same features.

They do get hot too... on the bottom of my 300-36 and Torker, you can see some discoloration from the heat all over the exhaust crossover, so it is functional.