I think so, but probably not reliably and/or for the long term.
In terms of the actual unmap call, the payload is in the munmap call, which is a syscall, and if you do have to set up the registers for that call, Go does have its assembler support which should be able to do that for you. You should be able to write Go source code that would perform that call, although you're going to be poking into some corners of Go most programmers never have to get into. You can also get to fuse, which in my experience is great at producing uninterruptible sleeps even when you're not trying to do it on purpose....
However, in terms of reliability and the long term, you have the problem that you're not the only thread in the program the way a C program can count on that, and if any of those other threads wake up and their memory is missing, it'll probably result in the process dying. You can do a couple things to try to avoid that a little, like pinning yourself to an OS thread and running the program in one CPU mode, but especially on the latest version of Go where they've implemented true pre-emption, you can't keep the runtime from running by just hogging the execution thread anymore.
So I suspect that as long as you win the race to unmap everything before the runtime wakes up (which may also require you to call sysmap through the assembly code directly, rather than using the syscall libraries as I'm pretty sure those notify the scheduler of what you're doing), you may be able to briefly be a process with no RAM mapped, but in human terms it won't be long before the runtime wakes up to do something, anything, and crash the process as a result. There's no way to avoid that in Go. You won't be able to have a process just sitting there indefinitely with no mapped RAM that you can admire and treasure and hand off to your children as part of their inheritance.
In terms of the actual unmap call, the payload is in the munmap call, which is a syscall, and if you do have to set up the registers for that call, Go does have its assembler support which should be able to do that for you. You should be able to write Go source code that would perform that call, although you're going to be poking into some corners of Go most programmers never have to get into. You can also get to fuse, which in my experience is great at producing uninterruptible sleeps even when you're not trying to do it on purpose....
However, in terms of reliability and the long term, you have the problem that you're not the only thread in the program the way a C program can count on that, and if any of those other threads wake up and their memory is missing, it'll probably result in the process dying. You can do a couple things to try to avoid that a little, like pinning yourself to an OS thread and running the program in one CPU mode, but especially on the latest version of Go where they've implemented true pre-emption, you can't keep the runtime from running by just hogging the execution thread anymore.
So I suspect that as long as you win the race to unmap everything before the runtime wakes up (which may also require you to call sysmap through the assembly code directly, rather than using the syscall libraries as I'm pretty sure those notify the scheduler of what you're doing), you may be able to briefly be a process with no RAM mapped, but in human terms it won't be long before the runtime wakes up to do something, anything, and crash the process as a result. There's no way to avoid that in Go. You won't be able to have a process just sitting there indefinitely with no mapped RAM that you can admire and treasure and hand off to your children as part of their inheritance.