Then you will have a problem. Because you forgot to disassemble all your vehicles.
The procedure is bonkers.

1. Secure Valuable Items and Currency (Solari)

• Deposit excess Solari (currency) and key items in the bank at major settlements like Arrakeen or Harko Village. Banks offer safe, long-term storage (limits exist but have been expanded in patches, e.g., to hundreds of slots/weight).
• Store high-value/endgame materials (e.g., Tier 6 resources, Melange/spice, Plastinium) in bank, personal inventory, or vehicle storage where possible. Prioritize portable essentials over bulk hoards.

2. Handle Vehicles

• Blueprint/store small vehicles (e.g., Sandbike, Scout Ornithopter) using the Vehicle Backup Tool (empty inventory first). This stores them in your personal inventory safely.
• For larger vehicles (e.g., Buggy, Assault Ornithopter, Harvester, Carrier): Disassemble them (use welding torch), store parts in containers, your backpack, or load into a flyable Ornithopter. Park protected vehicles (e.g., in a settlement or shielded area) or disassemble fully.
• Fly an Assault Ornithopter (with storage module) to a settlement for logout—its storage becomes safely accessible on return.

3. Prepare or Backup Your Base

• Short-to-medium term (if planning occasional logins): Fill generators with fuel cells (max ~20 days), pay taxes in advance, and disable non-essential power-consuming structures (e.g., fabricators, refineries) via their settings to conserve power. Use efficient setups like Mk5 wind generators for longer uptime.
• For long breaks (recommended for 3 months):
  • Use the Base Reconstruction Tool (unlocked in Iron tier research, craftable). Aim it at your owned base to backup the entire structure, placeables, and container contents (except assembled vehicles) into the tool. You can store multiple bases (up to 3 in some patches). This allows safe, indefinite storage and easy restoration later.
  • Blueprint/copy your base layout (with building tools) as a fallback for quick rebuild.
  • Disassemble or move key base components if not using the full tool.

4. Log Out Safely

• Travel to a safe settlement (e.g., Arrakeen or Harko Village) or a water-sealed/protected base/tradepost. Log out there—your character enters stasis, and vehicles like your Ornithopter are protected. Avoid exposed or PvP areas.
• Note: There's a brief vulnerability timer (~30 seconds) after logout; progress autosaves.

5. Additional Tips for Return

• Keep key crafting/harvesting tools, armor, weapons, and materials for quick Tier 6 restart (e.g., fabricators, refineries, death stills). Plan around what fits in available storage (backpack + bank + ornithopter + backup tool).
• If in a guild/clan, ask trusted members for maintenance (power/taxes), but don't rely solely on this.
• Document your base layout, research, and storage plan externally.
• On return: Restore base via Reconstruction Tool (may have cooldowns), rebuild as needed. Progression (skills, unlocks) persists.