Taking the right one to heaven is by no means a certainty! (5)
I believe the answer is:
risky
'by no means a certainty' is the definition.
I can't tell whether this definition defines the answer.
'taking the right one to heaven' is the wordplay.
'taking' is a deletion indicator.
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'right' becomes 'rt' (abbreviation as in Rt Hon- the Right Honourable).
'one' becomes 'i' (Roman numeral).
'to heaven' becomes 'sky' (I've seen this in another clue).
'rt' with 't' removed is 'r'.
'r'+'i'+'sky'='RISKY'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for risky that I've seen before include "Potentially dangerous" , "Having possibility of danger or loss" , "Unsafe" , "Hazardous" , "not playing safe" .)