The question is about what ‘should’ happen. In my opinion, the sentence should be determined based on the perpetrator’s intention.
However, sentencing in the US, UK and Australia allows for a life sentence for attempted murder. So the penalty for attempted murder CAN be the equivalent of the sentence for a successful murder.
In the US, “First-degree attempted murder carries greater penalties and often means a life sentence with the possibility of parole. Offenders typically spend at least 10 years in prison, although mandatory minimum sentences for attempting to murder a public official may be 10 to 15 years. Federal laws for attempting to kill a member of Congress or other federal official impose penalties ranging from 70 to 162 months.
Second-degree attempted murder penalties usually range from five years to 15 years in many states, depending on whether serious injury was inflicted. Sentences can be for longer periods if a firearm was used or if the crime was committed by a gang member or at the direction of a criminal gang. A prior criminal record will also enhance a sentence, even doubling it in states with “three strikes” laws, such as California”. (Legal Articles – Homicide)
In the UK, the Crown Prosecuting Page outlining sentencing guidelines for attempted murder states:-
“Level 1
The most serious offences including those which (if the charge had been murder) would come within para. 4 or para. 5 of schedule 21 to the Criminal Justice Act 2003 [see below for its terms)
Nature of offence: Serious and long term physical or psychological harm
Starting point: 30 years custody
Sentencing range: 27 – 35 years custody
Nature of offence: Some physical or psychological harm
Starting point: 20 years custody
Sentencing range: 17 – 25 years custody
Nature of offence: Little or no physical or psychological harm
Starting point: 15 years custody
Sentencing range: 12 – 20 years custody”.
In Qld, Australia, a person found guilty of attempted murder can be given life imprisonment.
Whether or not these sentences are applied is determined not only based on harm to the victim, but through an evaluation of pre-meditated intent. If you’re found to have intended to kill the victim, you could be sentenced to life imprisonment. That’s the maximum sentence in the UK and in Australia.