Hostage situations are a difficult balance of duty of care and general policing. Having to respect free passage should be optional if another opportunity to end the threat arises, As long as the hostage can be secured prior to engagement, or to prevent them from running off with the hostage still in their detainment, Officers should be allowed to, if authorised to by a supervisor, try and take down the threat. What you are suggesting is for even opportune moments to strike be disregarded, But for what? During free passage, officers allow a bunch of armed gunmen wanted for some of the most serious crimes to be allowed to leave and continue to pose a threat to the general public. Even if the hostage takers are warranted, Officers would have an extreme risk to their lives especially if they have to raid a property to get to them.
Limiting what officers can do further than what options they have already is not going to be an ideal set of circumstances if "Roleplay" is a concern. A hostage situation shouldn't be a forced powergame golden ticket out of every situation, more so should remain being a cornered last resort tactic criminals can resort to before turning to violence. If you really think having some forced get out of jail free card by threat of punishment if they successfully take you down at an opportune moment, Thats not roleplay, thats powergaming.
An elaborate hostage situation would normally result in guarenteed free passage with no pursuit, but a more spontaneous, poorly planned and executed one should receive the outcome it deserved. I'm not saying that all hostage situations should be planned meticulously in advance because I know thats not possible, But sometimes you're just stuck in shit creek without a paddle, as is life.
To say it'd encourage roleplay blurs the very definition of what RP is and implies that taking a window of opportunity to, as a police officer, end a violent standoff isn't roleplay, which is in itself a disregard for what it would mean to roleplay as a Police Officer. Being chained by your ankle to a set of rules that means you're forced to just give into every demand given and grant unrestricted free passage and agree with every single demand and deal made. Most "Hostage situation RP" is just cops saying "Okay sure I can offer you 5k and free passage because thats what some handbooks tell me to do", and shutting out any opportunity for a coordinated, well executed plan in stopping the hostage takers, which is their job at the end of the day, would absolutely not be the way forward in "preserving roleplay", it just leads to "SUPERVISOOOOOOOOOR THEY SHOT ME WHEN I HAD BEEN GIVEN FREE PASSAGE SUPERVISOOOOOOR POLICY 32.23 OF THE OFFICER RULES BOOK SAYS THEY CANT DO THAT".
Someone who takes a hostage alone or in small groups armed solely with Pistols should honestly achieve the level of success you'd expect them to; Stalled then shot in the side of the head the moment doing so becomes an almost guarenteed way to end the situation. This is the bulk of hostage situations, particularly the PD raid ones we saw a repeat string of constantly a few months back.
tl;dr: Hostage situations shouldn't be infallible, guarenteed golden tickets out of every interaction where you would normally be shooting Police to get out of, Police officers who launch realistic, coordinated attacks to apprehend or neutralise hostage takers at the right moment are in fact roleplaying as this is the Police's job, and this is not a good solution for tipping the scales of the interest in PVP VS Roleplay in favour of roleplay as it just forces something to go a specific way due to rules, forcing an unfairly significant advantage over the police force enforced by meta-knowledge that you will succeed 100% of the time or someones going to lose a PD rank or something like that is more of a problem than a solution.