Korean conjugation endings? (Stem + 고, 거나, 지만, etc)?

Everything that you listed is not very commonly used.

[가고] would be used in situations like:

우리는 [가고], 너의들은 남고.

(We [go], you guys stay.)

[가거나] would be used in situations like:

지금 [가거나], 나중에 [가거나].

([Go] now, or [go] later.)

[가지만] would be used in situations like:

우리는 지금 [가지만], 다음에 꼭 다시 올거야.

(We're [going] now, but we're definitely coming back.)

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You might have wanted to say things like these instead:

"Go and..."

For example, if you wanted to say 'Let us [go and play].'

Then it would be '우리 [가서 놀자].'

"Go or..."

For example, if you wanted to say 'Are we going to [go or not]?'

Then it would be '우리 [갈거야 말거야]?'

"Go but..."

For example, if you wanted to say 'I want to [go but I can't].'

Then it would be '난 [가고 싶지만 못가].'

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But these are also many other endings, such as:

가야하지만.../가야돼지만...

I need to go, but...

가면 안돼지만...

I shouldn't leave, but...

가서...

Go and...

가면...

When you go...

And more ^^