unfortunately this was a massive security and intelligence failure by Iran, and a major embarrassment
Israel said it will kill the leaders of the resistance wherever they are, and in recent days claim to have martyred Deif in Gaza, Shukr in Beirut, and Haniyeh in Tehran. they are making good of their promises.
Turkey is the only remaining safe option but Turkey is not willing to host Palestinian leaders and even Turkey doesn't offer full protection from Mossad assassinations. the difference is only the consequence of such an assassination, i.e., will Iran strike back directly.