[tjohns]

A pilot can legally land without a METAR, and this happens all the time. The stations can and do go offline. Sometimes they break, especially after a severe storm. Many smaller airfields don't have on-site weather reporting, some others don't have a network connection.

You look at the closest available weather station and you look at the forecasts — human-authored (TAFs) and computer-autored (GFA/MOS). And when you arrive, you look outside at the actual conditions — the windsock, actual flight visibility, etc. If the conditions are worse than expected, you divert to your alternate.