No missions will be unplayable, per se, but some missions will suddenly become hella-mad more difficult.
For instance, the first campaign mission is now nearly unbeatable as an Akula. Dunno about the 688i. For the RSR missions, "Holddown Exercise" will be extremely difficult (to say the least) if the RNG spawns a Kilo instead of a Foxtrot, which is subsequently out of range for the TA sonar.
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Vanvikan, Feb. 2009: ordinary human, KIA, night 4
HMS Thanatus, May 2009: ??? human, KIA, night 7
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