In most cases I would say it is worth it to try and salvage the string. I would be upset with myself if I gave up on the 2nd string and got 30 seconds for a malfunction that I could have cleared in 5-8 seconds, then on the 4th string run dry because I was all flustered about the 2nd string. Now I have two 30 seconds runs and one of them counts. I would much rather clear the malfunction or reload on the 2nd string, take my ~10 second time and call it a learning opportunity.
Now, ask me that on the 5th string when I rocked 1-4 and I might just take the 30 and avoid looking goofy fumbling with my gun and mags.