Operation with other fuels is not recommended, but operation with AVGAS for most Pratt & Whitney engines (Kingair PT6A-41,42) is acceptable in extenuating circumstances. Usually limited to a maximum combined total of 150hours in a single engine overhaul period.
Can't remember the SB # for the -41, 42 but for the -27, -28 etc check P&WC SB1244(Approved listing of fuels etc). The Caravan -114 will be similar. For the PW120 see the MM 72-00-00 4.E Table 13 for acceptable fuels, 4.F Table 14 for acceptable fuels restricted use, & 4.G Alternate emergency fuels (AVGAS)
In the end AVGAS has a different SG, & calorific value, & requires a greater temperature change to produce the same power as the recommended fuels. See higher ITT - increased hot end thermal distress.... sorry more $ per hour.
TT