My daughter lives in an Iowa college town in a 4 bedroom apartment, recently one of her roommates died from an asthma attack the landlord says the remaining 3 tenants still need to pay the total rent of $1150 divide by 3 instead of 4, unless they or the landlord finds someone else to sublease the apartment until May. Is this true?

It depends on how the lease is setup. If there is a single lease for the premises with the 4 roommates as co-tenants, then the landlord is correct. And the likelihood is that's how its written. He's renting a 4 bedroom apartment, not individual rooms. Therefore, he's entitled to the full monthly rent each month.

Only if he has separate leases for each room with use of common areas would he be wrong.

So they need to start looking for a new roomie quickly.

A new replacement person would be the best answer but they do not need to sublease. They can just move in and pay their share without signing a lease. That option may make it a bit easier to find someone. Otherwise the three tenants would likley owe the full amount for the term of the lease.