Question about Metal Gear 1987

Did Big Boss intend for Venom Snake to die? If so who is talking in the radio with Solid at the end telling him to turn around? Is it Venom? And if yes is he betraying Big Boss there?

And if Venom Snake was not supposed to die and Solid Snake was supposed to actually fail, what misinformation would big boss get out of there if Solid Snake would be dead?

Sorry if the questions are dumb but with MGSV everything got a little confusing to me.