It's hard to put a number on it. Drift increases exponentially with temperature and duration of exposure to elevated temperature. Humidity and thermal shock also contribute to drift. RTD's RTD's can also experience a certain amount of drift. However, they are much less susceptible to drift due to exposure at elevated temperatures than thermistors are.
Thermistors are available in point match and interchangeable varieties.
However, a number of configurations are available with regard to tolerance and temperature range. RTD's are classified by DIN specifications. Class A is also available upon request. If moisture protection is critical for your application, you may want to consider the hermetically sealed glass encapsulated DO-35 thermistor available from Alpha. However, if size or cost limitations force you to use chip and lead devices, Alpha can provide two forms of moisture protection.