The example text is correct and natural. Although the basic grammar books concentrate on five types of conditionals (types 0-3 and mixed), there are other conditionals. For a thorough but readable explanation, consult Practical English Usage by Swan.

Sentence #1: This sentence is acceptable for casual conversation but contains flaws that make it unsuitable for formal speech. The word "if" is logically imperfect. If "no one's reported him missing" is the reason for your supposition, then it might be better to use "because" or "since" rather than "if". Also, the double use of "suppose" is stylistically awkward. The two words actually refer to different suppositions: "suppose" refers to your own thinking, whereas "supposed" probably refers to what other people think. That is confusing by itself. But also, using the same word in one sentence for no compelling reason is generally to be avoided. Sentence #2: This sentence is good, but a comma is needed after "And" and there is an apostrophe at the end of the sentence that doesn't belong there. I personally try to avoid the word "get" because it says nothing specific. "Gets into the files" has no specific meaning. That does not mean it is wrong. "Get" means almost anything a speaker wants it to mean. For example, though unlikely, "gets into the files" could even mean "sneaks into the files and unlawfully changes the information that is there". Nobody is likely to interpret the sentence that way, but it does show how vacuous the word "get" is. There is almost always a better word available. For example, you could say "...before he is listed in the files" "...before his name enters the files" and so forth. I cannot suggest a best way because I really don't know what "gets into the files" is supposed to mean.