In this article I would like to present another grace view which I feel better fits the immediate context and Paul's use of the words salvation and work out. Believers are already eternally saved and cannot lose that salvation. While he does not use exactly those words, that is implicit in what he does say. Working out one's salvation is another way of talking about ongoing obedience. The following context bears out this conclusion.
Believers are thus to exercise ongoing obedience with an attitude of reverential fear.
Thus Paul may have used the word salvation metaphorically in v 19 to refer to a victorious triumph over the trials he faced by magnifying Christ through them whether he was released from prison or not. Zane Hodges, The Gospel Under Siege , Second Edition, pp. Second, it could refer to believers triumphantly glorifying Christ through temporal difficulties, whether they escaped them or not. In both cases temporal, not eternal, deliverance is in view. That is indeed the case.