Besides carrying out an expensive, extensive and integrated effort to preserve Bashar al Assad presidency position, the Islamic Republic of Iran is also coming up with conditions to keep its capability to utilize Syrian territory and possessions to look after its regional interests in case Assad regime falls. You can observe the information about Iran is Syria view this site.
The Iranian intelligence and security services are counseling and helping the Syrian military so as to retain Bashar al-Assad's regime. These attempts have changed to tactical training mission with the use of the Quds Force, Islamic Revolutionary Guards Corps Ground Forces, law enforcement services and intelligence services. In fact, it is said that the sending of Islamic Revolutionary Guards Corps Ground Forces to war abroad is meant to expand Tehran military might outside its borders.
Since the opposition in Syria has banned several ground supply networks between Damascus and Baghdad and the scarcity of Tehran port-visits in Syria, Iran have been supplying essential military equipment to Assad by air. For this reason, communication between Syria and Tehran is a key susceptibility for Iranian plans in Syria. As a matter of fact, Tehran wouldn't be able to support to Assad if this air route was banned via a no-fly zone. Pick out the most interesting info about Iran is Syria click here.
Further to this, Iran is assisting the pro-government shabiha mercenaries to partly prevent Assad's fall or its contraction into the coastal Alawite territory and Damascus. This makes the militias to become dependent on Iran and thus allowing Tehran to have some power and ability to project force and operate in Syria.
The Lebanese Hezbollah based group started taking direct combat position when it was clear that the Assad rule was losing much of its territory in the year 2012. What Hezbollah offered to Assad was a robust and well trained military troop whose participation in the war is in alignment with the Iranian strategic interests. However, the commitment from Hezbollah is not one hundred percent as the Hezbollah group has to balance its support of Syria and the domestic responsibilities that it has in Lebanon. Learn more details about Iran is Syria at https://en.wikipedia.org/wiki/Iran%E2%80%93Syria_relations.
The conflict in Syria has indeed constrained the influence Iranians held in the Levant and therefore, the collapse of Assad rule will prejudice Iran capability to display power. Hence the Iran strategy is to always ensure that it may continue pursuing its interest irrespective of whether the Assad's regime collapses or not. To make this a reality, Iran will use part of Syria as its command base provided that the Syria opposition forces do fail to establish total control over the entire Syrian territory.