In #5842, まさかの場合 should preferably be まさかの時は and in #5843, まさかの時 should be まさかの時は
There are 19 まさかの時 examples in WWWJDIC http://www.csse.monash.edu.au/~jwb/cgi-bin/wwwjdic.cgi?1Q%A4%DE%A4%B5%A4%AB%A4%CE%BB%FE_0__ which can be "borrowed" as necessary. In WWWJDIC examples the Japanese is usually good, but the English is sometimes dodgy.
a lot of those examples are duplicates, but i added the best. FYI the link on this page to "Search big database for more examples of まさかの〜" searches the same WWJDIC example database.
Wouldn't example [#5843] be more succinctly translated as, "If there is anything unexpected, please call."? It's not really necessary to include the "to this place" (or better - "here").