Yes.  Neodymium Iron Boron magnets are sensitive to heat.  If a magnet heated above its maximum operating temperature (176°F (80°C) for standard N grades) the magnet will permanently lose a fraction of its magnetic strength.  If they are heated above their Curie temperature (590°F (310°C) for standard N grades), they will lose all of their magnetic properties.  Different grades of neodymium different maximum operating and Curie temperatures. Yes.  Neodymium Iron Boron magnets are sensitive to heat.  If a magnet heated above its maximum operating temperature (176°F (80°C) for standard N grades) the magnet will permanently lose a fraction of its magnetic strength.  If they are heated above their Curie temperature (590°F (310°C) for standard N grades), they will lose all of their magnetic properties.  Different grades of neodymium different maximum operating and Curie temperatures. 

No, we don't, nor does anyone else, because they don't exist.  All magnets must have at least two poles.

Very little. Neodymium magnets are the strongest and most permanent magnets known to man. If they are not overheated or physically damaged, neodymium magnets will lose less than 1% of their strength over 10 years – not enough for you to notice unless you have very sensitive measuring equipment. They won't even lose their strength if they are held in repelling or attracting positions with other magnets over long periods of time.

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In most applications, the answer is simply "no". If the magnets will be exposed to higher temperatures while in repelling applications, the answer is "possibly". The exact answer is a bit too complicated for a FAQ answer, and requires specifics about the application.