Since your own translation is in Traditional Chinese, I used the same.
Besides, my translation is context-based (or I tried to make it that way), so some words are not literally translated. In case you want to learn more, further explanation is provided below.
We're leaving together
我們（要）一起離開
But still it's farewell
但這依然是離別
And maybe we'll come back
或許我們會再回來
To earth, who can tell
到地球上，誰能預料到？
I guess there is no one to blame
我想不該怪誰
We're leaving ground (leaving ground)
我們（將要）離開地面（離開地面）
Will things ever be the same again
一切還會像以前一樣嗎
It's the final countdown...
最後的倒數開始了...
The final countdown
最後的倒數
Ooh oh
噢噢
We're heading for Venus (Venus)
我們正往金星前進（金星）
And still we stand tall
而我們仍然堅挺
Cause maybe they've seen us
因為或許他們已經看到我們
And welcome us all (yeah)
且歡迎我們（是啊）
With so many light years to go
儘管有這麼多光年要走過
And things to be found (to be found)
還有這麼多事物去探索（去探索）
I'm sure that we'll all miss her so
我相信我們都會這麼想著它
It's the final countdown...
最後的倒數開始了...
我們（將要）一起離開
將要 is added to better visualize the moment.
誰能預料
The literal translation is 誰能告訴, but such translation does not make sense in Chinese. Besides, in this context, tell translates to 預料.
一切還會像以前一樣嗎
Things = 東西, but in this context, the meaning is probably (every)thing, which translates to 一切. Using 東西 itself as the subject does not make sense anyway.
最後的倒數開始了...
It's the final countdown here implies that the countdown has started, hence the phrase 開始了.
而我們仍然堅挺
Stand tall does not literally mean standing tall but rather being brave and proud. As such, 堅挺 or 堅強 or 挺立 are some more appropriate words here.
還有這麼多事物去探索
to be found literally means 被找到, but, in my opinion, it's probably more natural to say 去探索 or to seek/search for.
我相信我們都會這麼想著它
sure, in this context, means 相信; her(female) translates to 它(nonliving) because in Chinese, people usually don't use her to refer to, say, Earth, country, etc.
