The most common and most likely answer to this crossword clue is the 7 plus 2 letter word SOLDIER ON
I've seen this crossword clue in The Times
S
O
L
D
I
E
R
O
N
More clues leading to the result SOLDIER ON
- Persevere to end resistance in brief farewell
- Keep going private say, only with 50 per cent off
- Carry on Sergeant perhaps currently showing
- Old senior's prepared to keep going
- Persist as scrap metal merchant did, maybe conserving energy
- Tommy about to persevere
- Persevere at private playing
- Persevere? I’d sooner go crazy drinking lager top
- Persevere as small, ancient metal boxes start to explode
- Tommy planned to keep going
Buddy explains!

The straight part
We know that "Keep going" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case keep going = soldier on.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.