Literally all of the champions you listed have some pretty obvious forms of counterplay.
Ashe - Let your tank eat the arrow or dodge it since it's fairly slow moving. QSS.
Brand - Stay away from your teammates and minions. One person can carry the Pyroclasm away from everyone else if they're fast enough.
Darius - Don't let him get 5 stacks on someone or CC + disengage until his ultimate runs out. After level 16, CC him and/or build health.
Evelynn - Build MR and/or stay out of melee range. Have someone cover the backline so you can see what angles she's coming from and stay at mid to high HP.
Fizz- Dodge it, buy MR, let your tank eat the ultimate, stay away from the person being ulted, or use stasis. Very telegraphed.
Jarvan - Any sort of dash or blink. Ornn can also destroy his ult IIRC.
Karthus - MR, CC him if he's in vision, Zhonya's (Zhonya's CD is lower than Karthus' ultimate CD), or Edge of Night. Alternatively, heal and shield your way out of it since it will usually never do more than 1k (and that's in a best case scenario.
Lux - Dodge it and/or buy MR. Don't get rooted.
Malzahar - QSS or cleanse.
Nocturne - Stay out of vision and buy armor. His ultimate doesn't do that much damage, anyway.
Pyke - Literally any dash or heal. Stasis works well too. Kayle and Zilean ultimates can bait him really heavily as well.
Rek'sai - Armor, back off into your team.
Rengar - Back off into your team, armor, stasis, stay grouped up around your ADC or carry.
Sejuani - QSS, dodge it, let your tank facetank it.
Skarner - Don't let him get close. Displace him out of his ultimate, CC him so he can't drag the target away.
Talon - Stay grouped up around your ADC, armor, shields/heals.
Urgot - Bodyblock the ultimate, heal, stasis. IIRC QSS still works.
Varus - Bodyblock and back away from the initial target. QSS.
Veigar - Stay at high HP, build MR, stasis.
Vel'koz - Dodge it, CC him out of the ultimate, stasis, MR.
Zed - Stasis, dodge his other abilities.
#How are any of these an instant or guaranteed death?