If the Earth's magnetic field reverses in the near future will it cause a disaster?

It will cause problems... not necessarily any 'disaster'.... The magnetic field protects us against charged solar particles;  without it - or, with it switching and weakened in the process - more of those particles may penetrate our atmosphere & affect living tissues... so, there would likely be an increase in cancers. 

  It wouldn't wipe out humans, but it wouldn't be good for them, either. 

The last permanent reversal was only less than 800,000 years ago, when we went from "reversed" to our present polarity. Such reversals take a few thousand years to complete.

There was a flip around 41,000 years ago, when we went from normal to reversed, then back to normal again in a "very short time" (six hundred years or so). It is called the Laschamp Event. By now, it has been studied in many locations around the world (mostly through analysis of remaining magnetic signatures in lava flows). So far, we have found no sign of any increased death or sickness rates in any species (animal or plants).

Depends on how quickly the field flips to the opposite polarity.  The issue is that a fast flip will almost never be noticed.  But a slow flip can expose everyone to a cascase of charged particles because the magnetic field acts as a deflection shield for most gamma-induced secondary radiation.  On a slow magnetic flip, extra radiation might sneak its way in.

This does not happen quickly. Since there is no correlation of migratory species going extinct with magnetic polarity reversals, no there very likely will not be?disasters. That still does not explain the magnetic anomalies in the Bermuda and Dragon triangles. 

It never caused one before when it has reversed, so why would it cause a disaster now?

i would hope not

If the evidence we have from past reversals is any indication, no.  Life goes on pretty much without even noticing.

During the actual minimum during the reversal, there will probably be more sunburn and skin cancer cases, the Auroras will likely be visible further from the poles, and there could be some power grid outages.  But even that will probably not rise to the level of "disaster."

Fundamentally, no