This will work as well:

with SampleData as (

select

StrVal

from

(values ('abc ,'),('cde,xyz,aaa,'),('zzz, yyy ,ttt,'),('qwe'),('asd,fgh'))dt(StrVal)

)

select

StrVal,

left(StrVal,len(StrVal) - patindex(',%',reverse(StrVal)))

from

SampleData;