During file-and-rank infantry battles of yore; how receptive were soldiers to being put in the front line knowing their odds of dying would be substantially higher?

This depends on what period you mean. If you're looking for a Classical answer with the Greeks and Romans and all, this thread has answers from u/Iphikrates and u/Iguana_on_a_stick.

If you mean 1700s-onward Rev War/Napoleonic Wars musket battles, you'll want this section of the FAQ, the three subsections with 'Linear Tactics' in the name.